Patent Application
20180163246
The present disclosure relates to test devices, apparatuses and methods for detecting one or more analytes in a fluid sample. In particular, the present disclosure relates to methods and apparatuses suitable for processing data from a test device such as an electrochemical test strip. The present disclosure further relates to electrochemical test devices for determining concentrations of one or more analytes in a fluid sample.
The detection and measurement of substances, chemicals, or analytes in a bodily fluid sample is useful in a variety of applications, such as in fitness monitors or in the medical device industry. For example, an individual may choose to monitor a concentration of an analyte such as lactate in his or her bloodstream in order to determine whether or not a chosen fitness regime is effective.
As another example, people with diabetes need to regularly monitor the concentration of glucose in their bloodstream in order to determine if they are in need of glucose or insulin or other diabetes medication. Diagnostic devices and kits have been developed over the years to allow a diabetic individual to autonomously determine the concentration of glucose in their bloodstream, in order to better anticipate the onset of hyperglycaemia or hypoglycaemia and take any necessary action. These devices and kits are often referred to as Self-Monitoring of Blood Glucose (SMBG) devices and kits.
Another of the primary reasons why people with diabetes perform SMBG tests is to identify situations in which they may be at risk of ketoacidosis which is usually associated with very high blood glucose concentrations.
A severe insulin insufficiency (hypoinsulinaemia) is almost always also associated with sustained, highly elevated blood glucose concentration. Such hypoinsulinaemia can lead to the adverse condition diabetic ketoacidosis (DKA). Failure to detect DKA in a timely fashion or to appropriately manage this complication whenever it arises can result in a very serious medical emergency. Conversely if caught early enough and managed appropriately (e.g. with rehydration and therapeutic insulin), adverse outcomes can be fully mitigated, with medical emergencies prevented. Preventable hospitalisations and deaths can thus be avoided with a combination of relatively straightforward prophylactic measures and/or benign therapeutic interventions.
DKA is usually associated with blood glucose concentrations of greater than 300 mg/dl. Instances of DKA where the blood glucose concentration is less than 200 mg/dl have been relatively unusual.
Conventional approaches to DKA detection and prevention within non-clinical settings are based on first detecting high blood glucose by using SMBG measurement. Only when blood glucose is elevated, is the potential onset of DKA checked through subsequent measurement of blood or urinary ketones.
Therefore where ketoacidosis is associated with elevated blood glucose or where nausea, vomiting or abdominal pain is present, the subsequent presence of ketones and attendant risk of DKA should in theory be picked up by any user who diligently follows existing advice.
However, aside the fact that users may not always be diligent in following the recommendations as laid down, there remains a small but significant number of instances where ketoacidosis occurs in the absence of elevated blood glucose. This euglycaemic ketoacidosis can arise from metabolic changes resulting from, for example, carbohydrate restriction (which may result from starvation (e.g. associated with anorexia)), or diet (e.g. carbohydrate restricted diets), emesis (e.g. due to illness), or metabolic changes resulting from alcohol use or dependency, or metabolic changes occurring in pregnancy, or metabolic changes resulting from certain prescription drug use. In these instances a user could still miss a DKA event onset even where diligently following existing best advice.
Since it is the hypoinsulinaemia that stimulates the ketogenic pathways that ultimately results in DKA, irrespective of the actual blood glucose level, then any circumstances in which an insulin insufficiency coincides with low carbohydrate availability has the potential to result in a euglycaemic ketoacidosis event that could, with the currently existing standard of care, be susceptible to misdiagnosis for example, with the attendant increased risks of an adverse outcome for the sufferer.
Furthermore, some drugs including some diabetes management drugs may have the potential to increase the likelihood of DKA, and may also increase the likelihood that any such DKA is associated with euglycaemia.
For example, the SGLT2 inhibitor class of drugs (for example Dapagliflozon, Canagliflozin and Empagliflozin) have recently been licensed for use in diabetes management. These drugs work by increasing the amount of glucose from blood which is excreted through the kidneys. Their introduction has been associated with DKA as a possible side effect and several instances of SGLT2-associated DKA episodes have been associated with euglycaemia. As these highly effective drugs (and others with similar mode of action response profiles) become more widely adopted, there exists a concomitant danger of ever increasing occurrences of dangerous euglycaemic DKA episodes going undetected and untreated, with adverse outcomes for the patient.
Additionally, certain medications, including Biguanide drugs such as Metformin, Phenformin and Buformin (and including Metformin and SGLT2 inhibitor metformin combination therapies) have been linked with the occurrence of lactic acidosis. For example, a condition which has come to be designated as “MALA” (Metformin Associated Lactic Acidosis) has been identified. This exists within persons prescribed metformin based medications. Although rare, MALA is a life threatening complication, and if early detection and rapid treatment with haemodialysis is not effected, a mortality rate of up to 50% is known.
When trying to ascertain a level of an analyte in, for example, a blood sample, an individual will typically perform a finger stick using a lancing device to extract a small drop of blood from a finger or alternative site. An electrochemical test device, which is often a test strip, is then inserted into a diagnostic meter, and the sample is applied to the test strip. Through capillary action, the sample flows through a capillary channel across a measurement chamber of the device and into contact with one or more electrodes or conductive elements coated with sensing chemistry for interacting with a particular analyte or other specific chemical in the blood sample. The magnitude of the reaction is dependent on the concentration of the analyte in the blood sample. The diagnostic meter may detect the current generated by the reaction of the sensing chemistry with the analyte, and the result can be displayed to the individual.
Typically, such electrochemical test devices have a set of electrodes such as a counter/reference electrode and one or more working electrodes. Sensing chemistry is used which is typically tailored to the particular analyte or biometric of interest. An enzymatic electrode is a combination of an enzyme and an electrochemical transducer. The direct transfer of electrons between the enzyme and the electrode is generally not easy to achieve and so an electron transfer agent (or mediator) is sometimes used to transfer electrons between the enzyme and the electrode to facilitate the electrocatalysis. For example, when measuring the concentration of glucose in a sample, a glucose oxidase or a glucose dehydrogenase enzyme can be used in conjunction with a mediator such as potassium ferricyanide. When detecting other analytes, different enzymes may be used, such as β-hydroxybutyrate dehydrogenase for measuring the ketone body β-hydroxybutyrate or lactate oxidase for measuring lactate.
Conventionally, where highly elevated blood glucose readings occur within an SMBG measurement, users are often alerted to perform an additional check for the presence of ketone bodies either in their blood or urine. This enables the user to either ensure that DKA is not occurring, or to instigate appropriate and timely medical intervention in the event that DKA is occurring. At present, this necessitates the use of an additional separate test strip with an appropriate reagent chemistry which is distinct from the SMBG test strip itself. At present, users do not routinely screen for any risk of lactic acidosis in response to SMBG testing.
Whether ketone testing is done by urinalysis strips or by additional blood testing, conventionally, additional user steps, cost and inconvenience are involved for the user. Furthermore, some users may elect not to bother with the additional testing, and may miss the potentially dangerous onset of DKA as a result, and fail to treat appropriately, with the potential for adverse consequences.
A method of processing data from a test device is provided. The method may comprise determining a concentration of a first analyte in a fluid sample using first sensing chemistry. The first analyte may be an acidosis-related analyte. The method may further comprise determining a concentration of a second analyte in the fluid sample using second sensing chemistry. The second analyte may be glucose. The method may further comprise displaying a first indication related to the determined concentration of the second analyte. The method may further comprise, if the determined concentration of the first analyte is equal to or greater than a first threshold, providing a user-selectable option to display a second indication related to the determined concentration of the first analyte.
An acidosis-related analyte may be any analyte which may be associated with a reduction in pH or an increase in the anion gap within the blood, serum, plasma and other body tissues.
The anion gap is the difference between the measured cations (positively charged electrolytes) and measured anions (negatively charged electrolytes) within the sample, usually expressed in milliequivalents per litre (mEq/L).
By providing a method as described, high levels of acidosis-related analytes such as lactate or ketones may be detected and conveyed to a user, even when glucose levels in the fluid sample are not indicative of hyperglycaemia, for example when the glucose levels in the fluid are at a normal, euglycaemic, level. Accordingly, a user may be alerted to conditions such as euglycaemic DKA, which is where ketoacidosis occurs as a result of hypoinsulinaemia, even in the absence of hyperglycaemia, for example because of an insufficiency of carbohydrate intake.
An apparatus for processing data from a test device is disclosed. The apparatus may comprise a memory storing instructions to perform a method as disclosed herein. The apparatus may further comprise a processor which may be configured to perform the instructions stored in the memory. The apparatus may comprise circuitry for receiving an output signal generated from a fluid sample.
A machine-readable medium is disclosed. The machine-readable medium may have instructions stored thereon. The instructions may be configured such that when read by a machine, the instructions cause a method as disclosed herein to be carried out.
A system is disclosed. The system may comprise an apparatus as described herein for processing data from a test device. The system may further comprise a test device comprising a first working electrode having first sensing chemistry for detecting the first analyte; and a second working electrode having second sensing chemistry for detecting the second analyte.
An electrochemical test device for determining concentrations of multiple analytes in a fluid sample is disclosed. The electrochemical test device may comprise a first working electrode for first sensing chemistry for detecting a first analyte. The electrochemical test device may further comprise a second working electrode for second sensing chemistry for detecting a second analyte. The electrochemical test device may further comprise a third working electrode for third sensing chemistry for detecting a third analyte.
Examples described herein address the risk of DKA and enable effective early detection of DKA onset and prevention of DKA complications and hospitalisations, even where such DKA is associated with euglycaemic blood glucose readings. Other examples described herein address this risk and enable effective early detection of lactic acidosis onset and prevention of lactic acidosis associated complications and hospitalisations.
The risk of false alerts caused by spurious readings is minimised by utilisation of additional information pertaining to underlying risk factors, both acute and sustained, specific to a particular user.
A “Companion Health Management Tool” is disclosed which assists users, especially (although not exclusively) diabetic users, and their Health Care Professionals (HCPs) in managing their medications in such a way as to also optimise the benefit they receive from their condition-controlling medications while minimising the concomitant risk of potentially dangerous complications such as acidosis, over the medium to long term.
Additionally, there are disclosed devices and methods which facilitate early and easy disambiguation between distinct types of acidosis which may differ in their severity, optimum treatment protocols, and prognoses, such as lactic acidosis, diabetic ketoacidosis and euglycaemic ketoacidosis, and to thereby ensure that the most appropriate medical intervention can be delivered in a timely manner. For example severe lactic acidosis can warrant corrective haemodialysis treatment sometimes necessitating rapid hospitalisation, whereas mild DKA can often be self-managed or managed in a primary care setting with insulin and oral rehydration therapy. Euglycaemic ketoacidosis may require carbohydrate intake as well as insulin therapy, whereas in hyperglycaemic DKA, carbohydrate intake is specifically contra-indicated. Furthermore, where the underlying cause of DKA is potentially related to a specific medications, changes in dose or dosing frequency may be warranted, and disambiguation of the specific type of acidosis can be useful in establishing which medication needs to be adjusted. For example lactic acidosis in the absence of ketones may indicate that Biguanide medication might be the more likely implicated, whereas euglycaemic DKA might imply that SGLT2 medication is potentially the more likely implicated medication.
There is disclosed a blood ketone measurement which is effected simultaneously with the initial blood glucose test, optionally from the same sample, further optionally from within the same strip, with the user being advised automatically about the potential onset of DKA, in the event that an elevated blood ketone concentration had been detected, so that early detection and appropriate management and mitigation could be effected in the least deleterious manner.
There is disclosed a blood lactate measurement which is effected simultaneously with the initial blood glucose test, optionally from the same sample, further optionally from within the same strip, with the user being advised automatically about the potential onset of lactic acidosis, in the event that an elevated blood lactate concentration had been detected, so that early detection and appropriate management and mitigation could be effected in the least deleterious manner.
There is further disclosed a blood lactate measurement and a blood ketone measurement which are effected substantially simultaneously with the initial blood glucose test, optionally from the same sample, further optionally from within the same strip, with the user being advised automatically about the potential onset of any acidosis, with a concomitant disambiguation of the type of acidosis risk, in the event that an elevated blood lactate concentration or blood ketone concentration, or both had been detected, so that early detection and appropriate management and mitigation could be effected in the least deleterious manner.
There is further disclosed tracking and trending of measurements using such systems over a prolonged duration in conjunction with individualised information pertaining to specific acidosis risk factors and medication types and dosages, in such a way as to facilitate optimisation of treatment for the maximum benefit with respect to the underlying condition being treated, along with the simultaneous minimisation of acidosis episodes and other risk complications (e.g. hypoglycaemia).
Examples include a method and apparatus for the detection, prevention and management of ketoacidosis risks, including types of euglycaemic ketoacidosis, and ketoacidosis associated with medication.
Examples include a method and apparatus for the detection, prevention and management of lactic acidosis risks, including lactic acidosis associated with medication, for example diabetes medications which contain biguanide drugs such as metformin, phenformin or buformin.
Further examples include a method and apparatus for the substantially simultaneous detection, prevention and management of both ketoacidosis and lactic acidosis, with simultaneous disambiguation of the subtype of acidosis risk likely to be present.
Euglycaemic DKA is a fairly rare occurrence. There is therefore a need to distinguish between occasional spurious results that will inevitably occur, and genuine medical emergencies which need to be dealt with as a matter of urgency. Examples encompass apparatuses and systems which have been configured with appropriate methods to make such distinctions more easily possible.
Furthermore, because lactic acidosis is a fairly rare occurrence, there is a need to distinguish between occasional spurious results that will inevitably occur, and genuine medical emergencies which need to be dealt with as matter of urgency. Examples encompass apparatuses and systems which have been configured with appropriate methods to make such distinctions more easily possible.
Additionally, the apparatuses and systems disclosed herein can also be configured to include appropriate methods which enable medication (e.g. insulin, SGLT2 inhibitors, biguanides such as metformin and SGLT2/metformin combinations) to be titrated and dose adjusted and/or dose and time adjusted appropriately to ensure that adverse DKA events or lactic acidosis events can be avoided in the first instance, with treatment regimens thereby being optimised and individualised according to an individual's risk profile and user experience.
Examples include a meter and test strip for periodic simultaneous determination of blood glucose and blood β-hydroxybutyrate concentration. Other examples include a meter and test strip for the simultaneous determination of both blood glucose and blood lactate concentration. Further examples include a meter and test strip for the substantially simultaneous determination of blood lactate, blood β-hydroxybutyrate and blood glucose.
The present disclosure further provides a Companion Health Management tool within the test system that controls the communication of the blood glucose readings and/or blood ketone readings and/or blood lactate readings to the user and advises the user appropriately, based upon a combination of the individual measurements obtained and at least some the following elements:
(i) patient related information entered into the meter upon system set up by a user or health care professional (HCP), relevant to the risk of DKA or lactic acidosis;
(ii) prior meter readings;
(iii) user inputs in response to prompts;
(iv) event flags;
(v) trending information and/or averages captured by the meter across a series of measurements; and
(vi) configurable thresholds (CTs) set by the user and/or their HCP which enable alerting to be set according to individualised circumstances, medication types, dosages, and risk profiles.
The configurable thresholds of embodiments that control the alerting features are arranged to be modified and individualised in such a way that medication can thereby be optimally titrated so as to achieve the optimum balance of risk and benefit for a specific user according to their actual individual responses and measurements, (most likely, working in partnership with their HCP).
It is known that because of an individual's underlying metabolic health, risk factors, medication types and response history, the same measurement result across different individuals may have different underlying aetiologies and may necessitate very different courses of action. Readings which could signify the onset of a serious problem in one individual prompting a timely alert and appropriate medical intervention that could otherwise have been missed, could signify no problem in another with a different aetiology and any such alert would carry a nuisance value. The use of individually configurable thresholds for lactate and ketones alerts, in accordance with the present disclosure, allows users to tailor the system to their own metabolic profile and thereby maximise the value of any alerts while minimising the nuisance value of false alarms
The present disclosure describes improved methods of operating an apparatus or test meter for use with a multi-analyte electrochemical test device in order to monitor glucose and ketone levels. The present disclosure further describes a companion health management tool.
Further optional features will be appreciated from the following description.
Illustrative embodiments of the present disclosure will now be described, by way of example only, with reference to the drawings. In the drawings:
Throughout the description and the drawings, like reference numerals refer to like parts.
Whilst various embodiments of the invention are described below, the invention is not limited to these embodiments, and variations of these embodiments may be made without departing from the scope of the invention.
Throughout this specification, reference is made to directional terms such as “above” and “below”, or “upper” and “lower”. References made to such terms are purely indicative of relative positions of the features of embodiments disclosed herein. For example, wherever there is mention of a cover above a spacer layer and an insulator layer below the spacer layer, it should be understood that the cover and the insulator layer are formed on opposite sides of the spacer layer. That is, directional terms such as those described herein do not refer to a direction relative to a viewpoint of an observer, but instead should be considered in all aspects as relative terms.
Various additional details of aspects of electrochemical test devices are described in the following commonly assigned patent applications (denoted collectively herein as the “related applications”). These related applications include the United Kingdom patent application no. 1507506.2, entitled “Electrochemical test device” filed on 30 Apr. 2015; the United Kingdom patent application no. 1507507.0, entitled “Electrochemical test device” filed on 30 Apr. 2015; the United Kingdom patent application no. 1507508.8, entitled “Electrochemical test device” filed on 30 Apr. 2015; the United Kingdom patent application no. 1507452.9, entitled “Electron transfer agent” filed on 30 Apr. 2015; and the United Kingdom patent application no. 1507509.6, entitled “Electrochemical test device” filed on 30 Apr. 2015. The content of each of these related applications is hereby incorporated by reference herein in its entirety for all purposes.
The term “alkyl”, used alone or as part of a larger moiety, refers to a straight or branched chain aliphatic group having from 1 to 12 carbon atoms. The alkyl group therefore has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 carbon atoms. For purposes of the present disclosure, the term “alkyl” will be used when the carbon atom attaching the aliphatic group to the rest of the molecule is a saturated carbon atom. However, an alkyl group may include unsaturation at other carbon atoms. Thus, alkyl groups include, without limitation, methyl, ethyl, propyl, allyl, propargyl, butyl, pentyl, and hexyl.
The term “amine” may refer to a primary, secondary or tertiary amine. The amine will generally be NRR′R″, where R, R′ and R″ are each selected from hydrogen or alkyl. Any suitable alkyl group may be used. Preferred alkyl group will be C1, C2, C3, C4, C5, C6. Preferably, an amine is NH3.
The term “heteroaryl” means a monocyclic or bicyclic radical of 5 to 12 ring atoms having at least one aromatic ring containing one, two, or three ring heteroatoms selected from N, O or S, the remaining ring atoms being C. The attachment point of the heteroaryl radical may be via the heteroatom. The heteroaryl rings may be optionally substituted as defined herein. Examples of heteroaryl moieties include, but are not limited to, optionally substituted imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, oxadiazolyl, thiadiazolyl, pyrazinyl, thienyl, benzothienyl, thiophenyl, furanyl, pyranyl, pyridyl, pyrrolyl, pyrazolyl, pyrimidyl, quinolinyl, isoquinolinyl, benzofuryl, benzothiophenyl, benzothiopyranyl, benzimidazolyl, benzooxazolyl, benzooxadiazolyl, benzothiazolyl, benzothiadiazolyl, benzopyranyl, indolyl, isoindolyl, triazolyl, triazinyl, quinoxalinyl, purinyl, quinazolinyl, quinolizinyl, naphthyridinyl, pteridinyl, carbazolyl, azepinyl, diazepinyl, acridinyl and the like, including partially hydrogenated derivatives thereof.
The term “halide” refers to a substituent which is fluoro, chloro, bromo or iodo.
The term “substituted”, as used herein, means that a hydrogen radical of the designated moiety is replaced with the radical of a specified substituent, provided that the substitution results in a stable or chemically feasible compound. The phrase “one or more substituents”, as used herein, refers to a number of substituents that equals from one to the maximum number of substituents possible based on the number of available bonding sites, provided that the above conditions of stability and chemical feasibility are met. Unless otherwise indicated, an optionally substituted group may have a substituent at each substitutable position of the group, and the substituents may be either the same or different.
An electron transfer agent (or redox mediator) is an agent for transferring electrons between an analyte or an analyte-reduced or analyte-oxidized enzyme and an electrode, either directly, or via one or more additional electron transfer agents.
An electron transfer agent as disclosed herein may be distinguishable by its standard redox potential i.e. a standard hydrogen electrode (SHE) at Standard Temperature and Pressure (25° C. and 1 atm).
A method of processing data from a test device is disclosed. The method comprises determining a concentration of a first analyte in a fluid sample using first sensing chemistry, wherein the first analyte is an acidosis-related analyte. The method further comprises determining a concentration of a second analyte in the fluid sample using second sensing chemistry, wherein the second analyte is glucose. The method further comprises displaying a first indication related to the determined concentration of the second analyte. The method further comprises, if the determined concentration of the first analyte is equal to or greater than a first threshold, providing a user-selectable option to display a second indication related to the determined concentration of the first analyte.
The test device may be an electrochemical test device. The electrochemical test device may be a multi-analyte electrochemical test device.
The step of determining a concentration of a second analyte in the fluid sample may comprise determining that the concentration of the second analyte is indicative of euglycaemia.
The step of determining a concentration of a second analyte in the fluid sample may comprise determining that the concentration of the second analyte is less than or equal to 33 mmol/L and greater than or equal to 4 mmol/L.
The step of determining a concentration of a second analyte in the fluid sample may comprise determining that the concentration of the second analyte is less than or equal to 11 mmol/L and greater than or equal to 4 mmol/L.
The step of determining a concentration of a second analyte in the fluid sample may comprise determining that the concentration of the second analyte is indicative of hypoglycaemia.
The step of determining a concentration of a second analyte in the fluid sample may comprise determining that the concentration of the second analyte is indicative of hyperglycaemia.
The method may further comprise receiving user selection of the user-selectable option and, in response to receiving user selection of the user-selectable option, stopping display of the first indication and displaying the second indication.
Determining a concentration of a first analyte in the fluid sample may comprise determining that the concentration of the first analyte is indicative of an acidosis-related condition. The acidosis-related condition is diabetic ketoacidosis, DKA. The acidosis-related condition is euglycaemic diabetic ketoacidosis. The acidosis-related condition is Metformin associated lactic acidosis, MALA.
The first threshold may be a user definable threshold.
The first analyte may comprise a ketone body. The first analyte may comprise β-hydroxybutyrate. The first threshold may be about 0.1 mmol/L. The first threshold may be about 0.6 mmol/L. The first threshold may be about 1.5 mmol/L.
The first analyte may comprise lactate. The first threshold may be about 2.5 mmol/L. The first threshold may be about 3.5 mmol/L. The first threshold may be about 5 mmol/L.
If the determined concentration of the first analyte is greater than or equal to a second threshold, the second threshold being greater than the first threshold, the second indication may comprise a warning concerning the determined concentration of the first analyte.
The second threshold may be a user definable threshold. The second threshold may be about 0.6 mmol/L. The second threshold may be about 1.5 mmol/L. The second threshold may be about 3 mmol/L. The second threshold may be about 5 mmol/L. The second threshold may be about 4 mmol/L. The second threshold may be about 3.5 mmol/L.
The method may further comprise receiving input, wherein the input comprises at least a selection from the group comprising:
The method may further comprise receiving input, wherein the input comprises information pertaining to at least one of the following categories:
The method may further comprise logging the determined concentration of the first analyte and the determined concentration of the second analyte. The method may further comprise providing an indication of a trend in the logged determined concentration of the first analyte and the logged determined concentration of the second analyte.
The method may further comprise logging whether a transient risk of an acidosis-related condition was absent, present or not assessed.
The method may further comprise providing an output to display, the output comprising at least one of a prompt to repeat the test or an indication of a suspected condition of a user.
The first indication may comprise a numerical value. The first indication may comprise an informative symbol. The second indication may comprise a numerical value. The second indication may comprise an informative symbol.
The method may further comprise determining a concentration of a third analyte in the fluid sample using third sensing chemistry, wherein the third analyte is an acidosis-related analyte. The method may further comprise, if the determined concentration of the third analyte is equal to or greater than a third threshold, providing a user-selectable option to display a third indication related to the determined concentration of the third analyte.
The method may further comprise communicating with a third party, such as a health care provider, over a communications network.
An apparatus for processing data from a test device is provided. The apparatus comprises a memory storing instructions to perform a method as disclosed herein. The apparatus further comprises a processor configured to perform the instructions stored in the memory.
A machine-readable medium is provided having instructions stored thereon. The instructions are configured such that when read by a machine, the instructions cause a method as disclosed herein to be carried out.
A system is provided. The system comprises an apparatus for processing data from a test device, as disclosed herein. The system further comprises a test device comprising a first working electrode having first sensing chemistry for detecting the first analyte, and a second working electrode having second sensing chemistry for detecting the second analyte. The test device may be an electrochemical test device. The electrochemical test device may be a multi-analyte electrochemical test device. The test device may further comprise a third working electrode having third sensing chemistry for detecting a third analyte.
An electrochemical test device for determining concentrations of multiple analytes in a fluid sample is provided. The electrochemical test device comprises a first working electrode for first sensing chemistry for detecting a first analyte. The electrochemical test device further comprises a second working electrode for second sensing chemistry for detecting a second analyte. The electrochemical test device further comprises a third working electrode for third sensing chemistry for detecting a third analyte. The first working electrode may have sensing chemistry for detecting the first analyte. The second working electrode may have sensing chemistry for detecting the second analyte. The third working electrode may have sensing chemistry for detecting the third analyte. The first analyte may be an acidosis-related analyte. The first analyte may comprise a ketone body. The first analyte may comprise β-hydroxybutyrate. The second analyte may comprise glucose. The third analyte may be an acidosis-related analyte. The third analyte may comprise lactate.
Multiple configurable thresholds may be used. The table below shows example thresholds that may be used (units of concentration shown in mmol/L).
Accordingly, for a given analyte one or more configurable thresholds may be set. For example, when detecting blood ketones, a first threshold CT1 may be set at 0.6 mmol/L, and a second threshold CT2 may be set at 3 mmol/L. When a determined concentration of the ketones in a fluid sample is above CT1, a user-selectable option to display an indication related to the determined concentration of the ketones may be used. When a determined concentration of the ketones in the fluid sample is above CT2, the indication may comprise further information, such as a warning that the determined concentration of the ketones is high.
In some circumstances, it may be desirable to set further configurable thresholds, such as CT3 and CT4 shown in the table.
The electrochemical test strip 100 comprises a support layer or substrate 110. Substrate 110 has a thickness of around 0.35 mm. The substrate 110, in this example, is made from polyester, although any suitable substrate may be used. The substrate 110 is thermally and dimensionally stable, with consistent properties such as thickness, surface roughness and surface energy.
Above the substrate 110 is the conductor layer 112. In this example, the conductor layer 112 is directly disposed upon the substrate 110 using carbon-based ink. In this example, the conductor layer 112 is printed directly onto the upper surface of the substrate 110. The conductor layer 112 may be printed onto the substrate 110 using screen printing, lithographic printing, tomographic printing, sub-microlitre controlled volume drop on demand printing technologies, or any other suitable method of printing. The conductor layer comprises a set of electrodes including a first working electrode 114, counter/reference electrode 116, a second working electrode 118 and fill-sufficiency detect electrode 120. The conductor layer 112 further comprises a set of conductive tracks 122. In this example, the conductive tracks 122 extend along the longitudinal axis of the electrochemical test strip 100. The conductive tracks are suitable for electrically coupling the electrodes to an apparatus, or test meter, in order for the test meter to analyse currents produced by target analytes in the blood sample. The conductor layer 112 further comprises a switch-on bar 124 for activating the apparatus or test meter.
Above the conductor layer 112 is an insulator layer 126. The insulator layer 126 is made of an electrically insulating material, and is directly disposed upon the upper surface of the conductor layer 112. The insulator layer 126 is, in this example, made of a dielectric material and defines an interaction area. That is, the insulation layer 126 electrically insulates some portions of the conductor layer 112 from the layers situated above in the electrochemical test strip 100. Specially designed gaps in the insulator layer 126 expose some portions of the conductor layer 112 to the layers situated above in the electrochemical test strip 100. In this way, the insulator layer 126 defines which part or parts of the electrodes of the conductor layer 112 are able to come into contact with an applied blood sample for the measurement of the analyte.
Sensing chemistry is applied to the electrodes of the conductor layer 112. In this example, the sensing chemistry comprises four reagent layers 128, 130, 132 and 134 which are applied to exposed electrode interaction areas after the insulator layer 126 is formed. More or fewer reagent layers may be present. The first working electrode 114 has sensing chemistry (reagent layers 132 and 134) for a first analyte. A first reagent layer 128 is applied to both the second working electrode 118 and the counter/reference electrode 116. In this example, the first reagent layer 128 is also applied to the fill-sufficiency detect electrode 120. An additional analyte-sensitive layer 130 is applied to the second working electrode 118, the counter/reference electrode 116 and the fill-sufficiency detect electrode 120. In this way, the second working electrode 118 is provided with sensing chemistry for a second analyte. The sensing chemistry for the second working electrode 118 comprises suitable reagents for detecting the second analyte.
Although the reagent layers 132 and 134 are not shown to be in contact with the counter/reference electrode 116, they may also be in contact with the counter/reference electrode 116.
Above the insulator layer 126 is a spacer layer 136 formed of a polyester core. The spacer layer 136 defines a sample introduction channel 138, or measurement chamber, for introducing a blood sample to the conductor layer 112. The height of the sample introduction channel 138 is defined by the thickness of the spacer layer 136. The spacer layer 136 is formed of double sided adhesive tape which, in this example, is applied directly to the upper surface of the insulator layer 126. The sample introduction channel 138 is formed by providing a gap into the double sided adhesive tape of the spacer layer 136. The thickness of the spacer layer 136 is approximately 0.1 mm, which provides a good balance between the volume of the sample introduction channel 138 and the performance of the electrochemical test strip 100.
Above the spacer layer 136 is a cover layer 140. During manufacture, the spacer layer 136 and the cover layer 140 may be applied to the test strip 100 separately or as a single prelaminated layer, although in this example the cover layer 140 is a separate layer to the spacer layer 136. The cover layer 140 acts as a ceiling to the sample introduction channel 138, thereby substantially closing the sample introduction channel 138 from above. The cover layer 140 is formed of single sided tape and, in this example, is adhered directly to the upper surface of the spacer layer 136. The lower surface of the cover layer 140 has hydrophilic properties, which assist in drawing a blood sample into the sample introduction channel 138. The cover layer 140 further has a vent 142 suitable for venting air out of the sample introduction channel 138 to allow a blood sample to enter the sample introduction channel 138 via capillary action. The vent 142 is narrower than the sample introduction channel 138 so that air may easily vent from the sample introduction channel 138 but blood or any other fluid will not easily be able to pass through the vent 142.
In use, a fluid sample is provided to the electrochemical test device and a potential difference is applied across the fluid sample to generate a detectable output signal indicative of one or more analyte concentrations in the fluid sample. In this example, in use a blood sample is applied to the sample introduction channel 138 of the electrochemical test strip 100. Through capillary action, the blood is drawn into the sample introduction channel 138 to the electrodes 114, 116, 118 and 120 of the conductor layer 112. That is, the sample introduction channel 138 acts as a capillary channel. A potential difference is applied across the electrodes 114 and 116 and the blood sample, and the electrodes 118 and 116 and the blood sample, and output signals such as transient currents are generated from the blood sample. The characteristics of the output signal(s) can be used to determine the concentrations of one or more analytes, such as glucose, lactate or β-hydroxybutyrate, in the blood sample.
In the electrochemical test device 100 of
The cofactor 350 may be nicotinamide adenine dinucleotide phosphate (NADP+).
The diaphorase 340 and the entrapped mediator (320, 330) carry out the following reactions:
NADH+H++Mediator→NAD++Reduced Mediator (1)
NADPH+H++Mediator→NADP++Reduced Mediator (2)
Either NADH (the reduced form of NAD+) or NADPH may be used as reductants.
The diaphorase 340 may be any suitable diaphorase. For example, the diaphorase may be an NADPH:acceptor oxidoreductase (NADPH dehydrogenase of the class EC 1.6.99.1). The diaphorase may be an NADH:acceptor oxidoreductase (NADH dehydrogenase of the class EC 1.6.99.3). The diaphorase may be an NADH:(quinone acceptor) oxidoreductase (NADH dehydrogenase (quinone) of the class EC 1.6.99.5).
With reference to
In this example, the first working electrode 410 is coated in two layers 430, 440 of reagents. In particular, the reagent layer 430 comprises an electron transfer agent and a diaphorase. Reagent layer 440 comprises suitable reagents for reacting with a ketone in the sample. For example, reagent layer 440 comprises β-hydroxybutyrate dehydrogenase for reacting with β-hydroxybutyrate, and a cofactor for the β-hydroxybutyrate dehydrogenase such as NAD(P)+.
The second working electrode 420 is provided with two layers of sensing chemistry 450, 460. The layer 450 adjacent the second working electrode 420 comprises an electron transfer agent. Reagent layer 460 comprises a glucose oxidase for reacting with glucose in the sample.
Additionally, each layer of the sensing chemistry comprises suitable buffers, surfactants and other additives. For example, the sensing chemistry may comprise one or more of a buffer, a gelling or thickening agent such as hydroxyethyl cellulose (HEC) or other cellulosic polymers, a rheology/viscosity modifier such as silica, flavin mononucleotide (FMN) for stabilising the diaphorase and a surfactant such as Tween 20.
The electron transfer agents at each of the first and second working electrodes may be the same or different. Any suitable electron transfer agent may be used. For example, potassium ferricyanide may be used as an electron transfer agent. For example, ruthenium pentaammine chloride may be used as an electron transfer agent. For example, ruthenium hexaammine trichloride may be used as an electron transfer agent.
Potassium ferricyanide has a number of benefits as a mediator. In particular, potassium ferricyanide is highly water soluble, has a small molecular weight and fast homogeneous and heterogeneous kinetics. Accordingly potassium ferricyanide supports a large analyte measurement range.
Ruthenium pentaammine chloride has a number of benefits as an electron transfer agent. In particular, ruthenium pentaammine chloride has a standard redox potential of approximately −0.08 Volts. The standard redox potential for the NAD(P)+/NAD(P)H couple is approximately −0.315 Volts. Accordingly, ruthenium pentaammine chloride represents an overpotential with respect to the NAD(P)+/NAD(P)H redox couple of approximately 0.235 Volts. In order to achieve the high level of sensitivity that is required to measure, for example, blood ketones such as β-hydroxybutyrate (typically 0.1 mM) it is useful to choose a mediator with a low redox potential so that any interference due to the oxidation of opportunist species is reduced. Ruthenium pentaammine chloride is thus a good candidate for use in an electrode for measuring β-hydroxybutyrate. Furthermore, unlike some other compounds such as potassium ferricyanide, ruthenium pentaammine chloride does not react with surface amino acids present in the diaphorase which could lead to a deterioration of enzyme stability and therefore deterioration in electrode performance, and so the shelf life of the electrochemical test device is improved.
Ruthenium hexaammine trichloride has a standard redox potential of approximately 0.1 Volts, which corresponds to an overpotential with respect to the NAD(P)+/NAD(P)H redox couple of approximately 0.415 Volts. Accordingly, ruthenium hexaammine trichloride is a good candidate for use in an electrode for measuring blood ketones such as β-hydroxybutyrate, for which the sensitivity of the electrochemical test device is an issue. Additionally, ruthenium hexaammine trichloride does not react with surface amino acids in the diaphorase which could lead to a deterioration in electrode performance. In addition it is known that this molecule is stable over time, reacting little to, for example, moisture, sunlight, temperatures experienced during manufacture and conditions experienced in storage. Accordingly, the sensitivity of an electrochemical test device incorporating this mediator will not deteriorate rapidly over time.
The sensing chemistry may be applied in layers as illustrated in
In this example, the first working electrode 410 is coated in two layers 530, 540 of reagents. In particular, the reagent layer 530 comprises an electron transfer agent. Reagent layer 540 comprises suitable reagents for reacting with lactate in the sample. For example, reagent layer 540 comprises lactate oxidase for reacting with lactate.
The second working electrode 420 is provided with two layers of sensing chemistry 550, 560. The layer 550 adjacent the second working electrode 520 an electron transfer agent. Reagent layer 560 comprises a glucose oxidase for reacting with glucose in the sample.
The skilled person would appreciate that other variations of the sensing chemistry are possible. For example, there may be one or more reagent layers on each electrode. Layers 530 and 540 may contain both lactate oxidase and a mediator, such as potassium ferricyanide. Similarly, layers 550 and 560 may contain both glucose oxidase and a mediator such as potassium ferricyanide.
As with the example discussed above in relation to
Referring to the Figure, the meter 600 includes a number of user interfaces including a visual display 610 and a virtual or dedicated user input device 612. The meter 600 further includes a processor 614, a memory 616 and a power system 618. The meter 600 further comprises a communications module 620 for sending and receiving communications between processor 614 and remote systems. The meter 600 further comprises a port 622 for receiving an electrochemical test device which may be provided with a fluid sample to be analysed.
The processor 614 is configured to receive data, access the memory 616, and to act upon instructions received either from said memory 616, from communications module 620 or from user input device 612. The processor is further configured to control the application of potential differences across electrodes of an electrochemical test device when an electrochemical test device is docked in port 622, to receive output signals, such as transient current data, from the docked electrochemical test device, and to analyse said received output signals. The processor controls the display 610 and may communicate date to remote parties via communications module 620.
In use, a multi-analyte test strip such as electrochemical test strip 100 described above is received by port 622. The processor 614 causes a potential difference to be applied between the fill-sufficiency detect electrode 120 and the counter/reference electrode 116. A fluid sample, in this example a blood sample, is then applied to the electrochemical test strip 100 and flows through the sample introduction chamber 138 via capillary action towards the electrodes 114, 116, 118 and 120. Once a fill-sufficiency detect signal is detected by the processor 614, the fill-sufficiency detect signal indicative of the sample introduction chamber 138 being filled with the blood sample, the potential difference between the fill-sufficiency detect electrode 120 and the counter/reference electrode is turned off. A detection or measurement of one or more analytes in the blood sample can then be undertaken. In this example, the fill-sufficiency detect signal comprises a transient current signals.
The processor 614 controls the application of a potential difference between the first working electrode 114 and the counter/reference electrode 116 and further controls the application of a potential difference between the second working electrode 118 and the counter/reference electrode 116. Reactions between the sensing chemistry of the first working electrode 114 and a first analyte in the fluid sample generate a first output signal indicative of the concentration of the first analyte in the blood sample. Reactions between the sensing chemistry of the second working electrode 118 and a second analyte in the blood sample generate a second output signal indicative of the concentration of the second analyte in the blood sample. The first and second output signals may comprise transient current signals. The first and second output signals are received by the processor 614. The processor may then analyse the first and second output signals to determine a concentration of the first analyte in the blood sample and a concentration of the second analyte in the blood sample. Analysing the first and second output signals may comprise performing operations to account for sources of systematic error. For example, analysing the first and second output signals may comprise applying one or more algorithms to account for errors due to blood sample haematocrit at the first and second working electrodes.
The processor 614 is configured to output an indication of the determined glucose concentration to the display 610 on the test meter 600. If prompted, or in accordance with rules stored in the memory 616, the processor 614 may output an indication of the determined concentration of the first analyte to the display. If prompted, or in accordance with rules stored in the memory 616, the determined data may be communicated to an external device.
At step 720, a concentration of a second analyte in the fluid sample is determined using second sensing chemistry. The second analyte is glucose. As described above, the determination of the concentration of the glucose in the fluid sample may be made by applying a potential difference across a second working electrode (having second sensing chemistry comprising reagents suitable for reacting with glucose in the fluid sample) and the counter/reference electrode of the electrochemical test device. The second sensing chemistry may cause a second output signal such as a transient current to be generated, the second output signal indicative of a concentration of the glucose in the fluid sample. The second output signal may be processed or analysed by a processor on the apparatus.
The skilled person would appreciate that steps 710 and 720 may be performed in any order or at substantially the same time. For example, a determination may be made of the concentration of glucose in the fluid sample before a determination is made of the concentration of the first analyte in the fluid sample.
At step 730, a first indication related to the concentration of glucose in the fluid sample is displayed on user-readable display 610. The indication may comprise, for example, the determined concentration of the glucose in the fluid sample. The indication may comprise a message such as “high” to indicate that the concentration of the glucose in the fluid sample is higher than a glucose threshold and that the user should undertake mitigating or preventative actions to lower the level of glucose in their body. The indication may comprise a message such as “low” to indicate that the concentration of the glucose in the fluid sample is lower than a glucose threshold and that the user should undertake mitigating or preventative actions to raise the level of glucose in their body. The indication may comprise a message such as “normal” to indicate that the concentration of glucose in the fluid sample is neither high enough nor low enough to warrant extraordinary actions—that is, the determined glucose level indicates a euglycaemic condition of the user. The indication may also urge a user to seek medical attention where necessary.
At step 740 a determination is made as to whether the concentration of the first analyte is greater than or equal to a threshold. If the determined concentration of the first analyte is greater than or equal to the threshold then a user-selectable option is provided (step 740), to display a second indication related to the determined concentration of the first analyte. The user-selectable option may be in the form of an icon or button that may be selected by a user via the user input device 612. The user-selectable option may take any suitable form. The user selectable option may comprise, for example, displaying results, a colour indication, an information message, a warning, a recommendation for action, or an audible, vibrational, or wireless message. The user selectable option may comprise, for example, an informative symbol such as an arrow pointing upwards to indicate a high concentration of the first analyte or an increase in the concentration of the first analyte since a previous test was undertaken. An informative symbol may indicate that there has been no change in the concentration of the first analyte since a previous test was undertaken. An informative symbol may indicate that the concentration of the first analyte has decreased since a previous test was undertaken.
If the determined concentration of the first analyte is less than the threshold then no action is taken.
The skilled person would appreciate that, although at step 740, the condition for providing the user-selectable option is that the concentration of the first analyte is greater than or equal to a predetermined threshold, the condition may be that the first analyte is greater than a predetermined threshold. In examples, the method further comprises receiving user-selection of the predetermined threshold.
If both the concentration of the first analyte and the concentration of the second analyte are high then a user may be suffering from an acidosis-related condition such as hyperglycaemic ketoacidosis and may need to seek medical attention. If the concentration of the first analyte is high but the concentration of the second analyte is in the normal range, then a user may be at risk of an acidosis-related condition such as euglycaemic ketoacidosis and may need to seek medical attention.
At step 814, the determined concentration of glucose is compared against a first glucose threshold value, which in this example is 2.6 mmol/L. If the determined concentration of glucose is less than the first glucose threshold value, then a warning is displayed (step 816), the warning indicating that the concentration of glucose in the fluid is low. If the determined concentration of glucose is greater than or equal to the first glucose threshold value, then the method proceeds to step 818.
At step 818, the determined concentration of glucose is compared against a second glucose threshold value, which in this example is 4 mmol/L. If the determined concentration of glucose is greater than or equal to the first glucose threshold value and less than the second glucose threshold value then the determined glucose concentration is displayed (step 820). If the determined concentration of glucose is greater than or equal to the second glucose threshold value, then the method proceeds to step 822.
At step 822, the determined concentration of glucose is compared against a third glucose threshold value, which in this example is 11 mmol/L. If the determined concentration of glucose is greater than or equal to the second glucose threshold value and less than the third glucose threshold value, then the method proceeds to step 824. At step 824, the determined concentration of the ketone is compared with a first ketone threshold value. The first ketone threshold value is set by the user, optionally, set by a user from a default, pre-programmed value. For this example, it is assumed that the first threshold ketone value is 0.1 mmol/L, although other values may be chosen, for example, 0.6 mmol/L. If the determined concentration of the ketone is less than the first ketone threshold value, then the determined concentration of the glucose is displayed (step 826). If, however, the determined concentration of the ketone is greater than or equal to the first ketone threshold value then the method proceeds to step 828.
At step 828, the determined concentration of the ketone is compared with a second ketone threshold value. As with the first ketone threshold value, the second ketone threshold value is set by the user, optionally, set by a user from a default, pre-programmed value. For this example, it is assumed that the second ketone threshold value is 3 mmol/L, although any threshold value, for example 5 mmol/L, may be selected. If the determined concentration of the ketone is greater than or equal to the first ketone threshold value and less than or equal to the second ketone threshold value, then the determined concentration of glucose is displayed (step 830). Additionally, a user-selectable option is provided at step 830 for displaying the determined ketone concentration value. If, however, the determined concentration of the ketone is greater than the second ketone threshold value then the method proceeds to step 832. At step 832, the determined concentration of the glucose is displayed. Additionally, at step 832, a user-selectable option is provided for displaying the determined ketone concentration value. Additionally, at step 832, an indication is provided that the ketone concentration value is above the second ketone threshold value, and therefore it may be in the user's interest to select the user-selectable option for displaying the determined ketone concentration value.
Returning to consider step 822, if the determined concentration of the glucose is greater than the third glucose threshold value, then the method proceeds to step 834. At step 834, the determined concentration of the glucose is compared with a fourth glucose threshold value, which in this example is 33 mmol/L. If the determined concentration of the glucose is greater than or equal to the third glucose threshold value and is less than the fourth glucose threshold value then the method proceeds to step 836. At step 836 the determined concentration of the ketone is compared with the first ketone threshold value. If the determined concentration of the ketone is less than the first ketone threshold value, then the determined concentration of the glucose is displayed (step 838). If, however, the determined concentration of the ketone is greater than or equal to the first ketone threshold value then the method proceeds to step 840.
At step 840, the determined concentration of the ketone is compared with the second ketone threshold value. If the determined concentration of the ketone is greater than or equal to the first ketone threshold value and less than or equal to the second ketone threshold value, then the determined concentration of glucose is displayed (step 842). Additionally, a user-selectable option is provided at step 842 for displaying the determined ketone concentration value. If, however, the determined concentration of the ketone is greater than the second ketone threshold value then the method proceeds to step 844. At step 844, the determined concentration of the glucose is displayed. Additionally, at step 844, a user-selectable option is provided for displaying the determined ketone concentration value. Additionally, at step 844, an indication is provided that the ketone concentration value is above the second ketone threshold value, and therefore it may be in the user's interest to select the user-selectable option for displaying the determined ketone concentration value.
Returning to consider step 834, if the determined concentration of the glucose is above the fourth glucose concentration value then the method proceeds to step 846. At step 846 the determined concentration of the ketone is compared with the first ketone threshold value. If the determined concentration of the ketone is less than the first ketone threshold value, then a warning is displayed, the warning indicating that the determined concentration of the glucose is greater than the fourth glucose threshold value (step 848). If, however, the determined concentration of the ketone is greater than or equal to the first ketone threshold value then the method proceeds to step 850.
At step 850, the determined concentration of the ketone is compared with the second ketone threshold value. If the determined concentration of the ketone is greater than or equal to the first ketone threshold value and less than or equal to the second ketone threshold value, then a warning is displayed, the warning indicating that the determined concentration of the glucose is greater than the fourth glucose threshold value (step 852). Additionally, a user-selectable option is provided at step 852 for displaying the determined ketone concentration value. If, however, the determined concentration of the ketone is greater than the second ketone threshold value then the method proceeds to step 854. At step 854, a warning is displayed, the warning indicating that the determined concentration of the glucose is greater than the fourth glucose threshold value. Additionally, at step 854, a user-selectable option is provided for displaying the determined ketone concentration value. Additionally, at step 854, an indication is provided that the ketone concentration value is above the second ketone threshold value, and therefore it may be in the user's interest to select the user-selectable option for displaying the determined ketone concentration value.
An example system is now described. The example system relates to measurements of β-hydroxybutyrate and glucose for the detection, management and prevention of DKA including euglycaemic DKA. Further examples can alternatively or additionally include measurements of lactate for the detection, management and prevention of lactic acidosis.
When the system is set up initially for the patient a series of ‘Background Settings’ are configured which inform the system of any likely euglycaemic DKA and/or lactic acidosis risk factors.
In an example, these settings include at least one setting selected from the group comprising:
(i) whether the user is pregnant/has gestational diabetes;
(ii) whether the user is prescribed insulin, and optionally the dose taken, the type of insulin (fast acting, long acting, single dose, multiple daily injections, pump user etc), as well as optionally the insulin sensitivity factor of the individual;
(iii) whether the user is prescribed SGLT2 medication (and optionally the dose taken);
(iv) whether the user is prescribed metformin or SGLT2 inhibitor metformin combination therapy;
(v) whether the user suffers from alcohol dependency;
(vi) whether the user suffers from an eating disorder such as anorexia or bulimia (including diabulimia);
(vii) whether the user is following a carbohydrate restricted diet; and
(viii) whether the user has previously experienced a DKA episode in the absence of elevated blood glucose.
In an example, when DKA is considered a risk and ketones and glucose are simultaneously measured, if a positive response is elicited to any of questions (i), (iii), (iv), (v), (vi) or (vii) above, the system shall subsequently operate in a manner which is consistent with a sustained higher risk of euglycaemic DKA.
If a negative response is elicited to all of the questions except (ii), the system operates in a manner which is consistent with no sustained higher risk of euglycaemic DKA.
System Behaviour in Normal Use—where Previous 3 Tests have not Suggested DKA
Whenever a test is performed, in all instances the glucose result will be communicated to the user immediately after completion of the test. Thereafter, the subsequent response from the system to the user is governed according to the following algorithms, based upon the measured ketone and glucose results.
A high level process flow is shown in
At step 930 a fluid sample test is performed. At step 970 an indication representative of a determined glucose concentration is communicated to the user. At step 940 a “condition indicated” is determined internally by the system but not communicated to the user. The ‘condition indicated’ is determined based upon configurable thresholds set by the user and the analyte measurements determined in the test performed. One illustrative example of how the ‘condition indicated’ may be derived from the results of 930 and the thresholds set is shown in the “Condition Indicated” Boolean logic table shown subsequently.
At step 980, an indication, (including for example a warning) related to a determined concentration of ketones in the fluid sample is displayed if the “condition indicated” at 940 corresponds with a severe risk of DKA. Otherwise either the user will be prompted for additional input at step 990, if the “condition indicated” at step 940 determines that such additional user input is warranted, or else a “condition assessed” may be determined directly. A non-limiting function of the additional information input from 990 is to allow a risk of transient euglycaemic DKA (or “transient DKA risk”) to be assessed at step 995, in those cases where the “condition indicated” at 940 corresponds to a situation where such a ‘transient DKA risk’ determination is deemed to be necessary. For example if initially the “Condition Assessed” (950) logic initially produced a result which was “uncertain” in the absence of this supplementary input, then the additional input (990) and “transient DKA risk” (995) steps would be instigated by the system. At step 950 a “condition assessed” is determined internally by the system, based upon the combination of the ‘condition indicated’ at step 940 (from the analyte readings), as well as from the “sustained euglyclaemic DKA risk level” determined at 920 and in addition, if appropriate, ultimately from the ‘transient euglycaemic DKA risk’ which may by then have been assessed at step 995. One illustrative example of how the ‘Condition Assessed’ may be derived from the “Condition Indicated” (940) and the user specific information (910, 920 and if appropriate 990, 995) is shown in the “Condition Assessed” Boolean logic tables shown subsequently:
“Condition Indicated” Boolean Logic Table
As previously stated, in the first instance, a “condition indicated’ is determined, for example according to the ‘Condition Indicated’ Boolean logic table shown below:
In this case CT1 represents a first user definable, or configurable threshold concentration for example 0.6 mmol/L, below which concentrations are considered at a level which the user would not be too concerned about. Similarly CT2 represents a user definable, or configurable, threshold above CT1 but below which the user should wish to be informed of the ketone concentration, so as to take avoiding action with the aim of preventing a complication from developing (e.g. <1.5 mmol/L for β-hydroxybutyrate) and above which the user should aim to treat the complication that has developed or is developing. CT3 represents a third user definable, or configurable, threshold above which the complication has reached a point where immediate acute treatment and/or emergency action may be warranted, for example 3 mmol/L for β-hydroxybutyrate.
In the case of Lactate rather than β-hydroxybutyrate, and example threshold for CT1 would be 2.5 mmol/L, and an example setting for CT2 would be 3.5 mmol/L, and an example setting for CT3 would be 5 mmol/L.
The result reported to the user and the recommended advice they are given by the system will subsequently be arrived at on the basis of the ‘Condition Assessed’, which in turn is arrived at on the basis of the combination of the ‘Condition Indicated’ (940) along with the background information contained within the meter from initial set up (910, 920), and in some circumstances also in conjunction with the determination of any increase in ‘transient risk’ of (euglycaemic) DKA (995), which is suggested from responses to appropriate user prompts (990).
In the event that the user's immediately previous 1-3 test results all indicate that DKA risk was not present, an example of how the “Condition assessed” will initially be determined is shown in the on the following table.
“Condition Assessed” Boolean Logic Table: No Imminent DKA Risk Already Present (950)”:
In the event that the condition initially assessed is uncertain, it is then that the ‘transient’ risk of DKA will subsequently be determined by the system on the basis of user inputs (990, 995) in response to prompts such as questions on symptoms.
In the event that the condition indicated is ‘mild or moderate DKA risk’ and ‘no sustained high risk’ of DKA was previously identified, the ‘transient risk’ of DKA will be determined in the first instance (990, 995) by the system through user inputs in response to prompts, before any ketone results and advice are communicated to the user (960).
However, in the event that the condition indicated is severe DKA risk, the ketone result will first be communicated immediately to the user (980), before any transient risk of DKA is determined and appropriate advice subsequently communicated to the user (995, 960).
Determination of Transient DKA Risk (995)
Wherever appropriate, the transient risk of DKA will be assessed by the system based on the user's response to on screen prompts or questions such as in the following examples:
Q1. Have you been in a state of fast (no calorific intake) for the previous 6 hours OR have you been in a state of carbohydrate intake restriction (<˜100 g Carbohydrate) for the previous 24 Hours? (Y/N)
Q2. Have you consumed and excess of alcohol within the previous 24 hours (Y/N)
Q3. Have you suffered from nausea, vomiting, abdominal pain, shortness of breath, excessive urination, or mental confusion within the previous 12 hours (Y/N)
Q4. Have you been undertaking sustained vigorous exercise/exertion within the previous 3 hours? (Y/N)
In particular, Q4 above is intended to determine whether a user has undertaken anaerobic exercise which may be a cause of increased lactic acid.
An affirmative response to any of these questions results in the determination that there is a positive ‘transient elevated risk of DKA or EuDKA’ (995). A negative response to all of these questions results in a determination that there is negative transient elevated risk of DKA or Euglycaemic ketoacidosis (995).
In examples, the condition which had initially been assessed as “uncertain” is then revised as follows:
“Condition Assessed” Boolean Logic Table: No Sustained DKA Risk—where Initial “Condition Assessed” was “Uncertain”:
System Behaviour in “DKA Management Mode”—where One or More of the Previous 3 Tests have Suggested DKA is Possible:
In the event that any of the previous three results indicated that DKA risk was already present the Condition Assessed will be determined using different logic, for example as follows:
“Condition Assessed” Boolean Logic Table: Imminent DKA Risk was Already Present”:
Results Reporting and Advice to User:
Based on the “condition assessed”, the system will report and advise the user appropriately, for example as follows
The example logic employed here and the use in combination of the analyte measurements, the persistent risk factors specific to the individual and entered upon meter set up, and the transient risk factors optionally entered in response to user prompting, by which the system is able to progress from the ‘condition indicated’ state to the ‘condition assessed’ state demonstrates means by which the annoyance of spurious alerts may be more easily avoided whilst ensuring genuine alerts may be more readily identified.
This specific logic described is by way of example only, and other algorithms of this type can readily be envisaged by those skilled in the art.
The example above describes one specific illustration pertaining to the scenario with respect to ketoacidosis, especially diabetic ketoacidosis including euglycaemic ketoacidosis, based upon appropriate configurable thresholds, persistent risk factors and transient risk factors pertaining to that specific condition and known aetiologies.
The present disclosure is not limited to ketoacidosis associated with diabetes, and other causes of ketoacidosis might also be managed with similar methodology and appropriate algorithms, for example those susceptible to alcoholic ketoacidosis or those ketoacidoses associated with eating disorders.
Comparable logic can be employed in the case of lactic acidosis by use of a combined lactic acid and glucose sensor for the management of lactic acidosis, for example Metformin Associated Lactic Acidosis (MALA), based upon appropriate configurable thresholds, persistent risk factors and transient risk factors pertaining to that specific condition and its known aetiologies.
Furthermore, disambiguation between lactic acidosis (eg MALA) and diabetic ketoacidosis can be accomplished where both lactate and ketones are simultaneously assessed, and the appropriate recommendations presented based on whichever aetiology is determined on the basis of medications and measurements.
Companion Health Management System
The present disclosure further provides a companion health management system. The Companion Health Management system creates and maintains a time stamped log of, for example, the following parameters for each test:
1. Glucose result
2. Ketone result
3. Condition Assessed
4. Whether transient risk was absent, present or not assessed.
Trending and Medication Management with Companion Health Management System:
The results log may then be used by the Companion Health Management system to make ongoing recommendations based on best practice guidelines stored therein, and to thereby assist users and their health care providers (HCPs) to adjust therapy accordingly.
For example the following table shows example recommendations that may be made to the user by the system on the basis of results stored within the result log triggering accomplished in the example given above, by looking at the data from across a suitable review period, accessed by means of a ‘review history’ menu option:
In some examples, this is achieved by the system looking at the weekly, fortnightly or monthly averages and events logs compared across for example, a 3 week, 6 week or 3 month period, to establish the trends, conditions assessed, medications being taken and the risk factors (transient or sustained) present for the individual user.
In the case of the individual lay user, the health management system may output a cursory message which while appropriate may be of limited complexity and low informational burden, since this would be the most appropriate system response to that situation.
Beneath this high level message however, there may also be the option to review in detail all of the results, the conditions assessed, the user responses entered at the time (e.g. whether fasting or emesis was present) and event flags, such that an advanced user or HCP could spot underlying causes among the detail that was automatically captured by the Companion Health Management system at the time tests were performed (and which otherwise would be lost to the vagaries and subjectivity of the user's own recollection) and make recommendations accordingly.
The above schema gives one example of a Companion Health Management tool that uses the conditions assessed and the measurements made and medication type to provide substantially optimal ongoing management to an example user.
In this case, the system has the capability to differentiate appropriately between for example the following cases, and in each case advise accordingly:
Alternate management schema which are based on lactate results and lactic acidosis aetiologies can be similarly derived by those skilled in the art in light of the present disclosure. Concentrations of analytes in a fluid sample may be provided to a user in any suitable units. For example, a concentration may be provided in units of mg/dL. For example, a concentration may be provided in units of mmol/L.
Another condition that can be considered either in addition to or as an alternative to the scenario described above relates to lactic acidosis instead of ketoacidosis, and specifically to lactic acidosis where MALA may be a consideration.
In this situation the “Condition indicated” and/or “Condition Assessed” may be the existence or onset of MALA.
Alternatively, the conditions indicated and/or condition assessed may be suspected lactic acidosis induced by sepsis or ischemia, or alternatively, benign transient lactate elevation caused by strenuous exercise.
The “sustained risk factors” assessed for MALA in this situation would include, for example: biguanide based medications such as metformin, phenformin, or buformin, along with any other indications or patient history that could be indicative as to the possibility of impaired renal function, such as kidney function test results to cite one example.
The transient risk factors for MALA in this situation could include, for example, dehydration and emesis and such other factors as could be indicative of acute renal impairment.
The flow chart in
In the event of undetected Metformin Associated Lactic Acidosis (MALA), hospitalisation is almost inevitable and a serious risk of death is present (1310).
With appropriate use of the present disclosure as described, disambiguation between MALA and sepsis or ischemia related acidosis becomes facile, and appropriate and timely treatment for whichever condition is actually identified (at an intervention level which may be far below that of the Emergency Room) becomes enabled.
If a lactic acid build-up is detected then appropriate action may be taken. For example, if a concentration of lactic acid is above a threshold then a user may be provided with an indication related to the determined concentration of lactic acid. Configurable thresholds for Lactate (CT1, CT2, CT3) could be set at, for example, 2.5 mmol/L, 3.5 mmol/L and 5 mmol/L respectively, depending upon the individual user's metabolism and risk profile.
In this case, the transient risk factors, user prompts and selectable user inputs would be configured with logic such that elevated lactate produced in a benign fashion in the muscles merely as a response to vigorous exertion that was dissipated quickly (within a few hours) was readily identified and disambiguated from elevated lactate that was the result of a more sinister cause. This could be effected by means of establishing the presence of a sustained elevation of or upward trend in lactate in the absence of exertion through, for example, prompting the user to conduct timely follow up testing after a period of rest or low intensity exertion, for example as outlined in the flow chart in
For example, if a lactic acid build-up is detected at step 1308, then a user may stop taking Metformin and/or rehydrate (1312). If the user's lactate levels increase or remain elevated (1314) then sepsis of ischemia may be suspected a medical treatment may be sought (1316).
The potential onset of MALA and its disambiguation from, for example, ischemia or sepsis related Lactic acidosis (both of which would necessitate their own appropriate care and management) would be established through the absence of evidence of sepsis or ischemia related symptoms (e.g. chest pains, breathlessness, infection, etc.) after the user was prompted to identify the presence or absence of such symptoms in the situation where elevated lactate readings had been detected by the system, as well as by the trend towards normalisation of lactate levels that followed on from the (possibly temporary) cessation of bigunaide (e.g. metformin) therapy. This could be accomplished by identifying an upward trend or sustained elevation in lactate level in the absence of exertion, rather than relying on a single high reading that subsequently reduced when the user was sedentary. Additionally by advising users to at least temporarily desist from their metformin therapy, MALA could potentially be avoided altogether and the underlying cause of the lactic acidosis within that user (e.g. cumulative build-up of biguanides due to inadequate excretion of these by the kidneys) thereby more readily identified.
If, after desisting from taking Metformin and/or rehydrating, a user's lactate levels normalise (1318) then lactic acidosis and hospitalisation may be avoided (1320). After kidney function tests if appropriate (1322) to determine that a user's kidney functions have returned to normal, a user may resume taking Metformin (1324) and tests may be taken over time to verify that the user's lactate levels stay low (1326).
Example symptoms and conditions indicative of ischemia or sepsis that the system would prompt the user to highlight when moving from the ‘condition indicated’ to the ‘condition assessed’ determination, and in accomplishing the disambiguation of the acidosis type could include, for example:
Example “Sustained” risk factors for MALA would include:
Transient risk factors for MALA would include:
“Conditions assessed” by the system thereby would include, for example:
Normal: Euglycaemia and lactate below CT1;
Hypoglycaemia: Any SMBG reading <4 mmol/L;
Hyperglycaemia: →based upon blood glucose readings in the absence of elevated lactate;
Possible DKA risk: (no elevated lactate in the presence of ketonurea or elevated blood ketones and high blood glucose readings);
Severe DKA risk→elevated lactate in the presence of ketonurea or elevated blood ketones and high blood glucose readings;
Exertion based lactate→transient lactate elevation which trends towards normal after a sedentary period;
Sepsis or ischemia based Lactic acidosis→elevated lactate which is sustained or increasing in the absence of exertion, in the absence of metformin therapy, or which does not reverse upon metformin discontinuation and/or exists in the presence of other ischemia or sepsis indications; and
Possible MALA onset: elevated lactate levels in the absence of sepsis or ischemia symptoms which corrects upon discontinuation of metformin.
A process flow such as that shown in
During set up of the system, at step 1402, an indication is made by a power user or health care provider as to whether the patient or user is taking Metformin or another biguanide-based medication.
In the event that a test detected an elevated lactate level (1404) the patient or user is invited to indicate whether or not they have performed recent strenuous anaerobic exercise (1406). If the user indicates that they have performed recent strenuous exercise, then there is a possibility that the elevated lactate result of step 1404 is the result of anaerobic respiration arising from physical exertion. In the incidence of recent physical exertion being confirmed by the user, a retest after a sedentary period is prompted (1408). A retest is performed (1410) and if this retest indicated a trend towards normalisation of lactate levels, the elevated lactate reading is disregarded as a benign instance of anaerobic respiration (1412).
If a retest at step 1410 indicates that the user's lactate levels are not normalising, then at step 1414 then the user instigates a hiatus in the Metformin or other biguanide-based therapy. If the user's lactate levels normalise after this (step 1434) then the user's kidney functions are checked (1436) before resuming Metformin or other biguanide-based medication.
If at step 1406 the user indicated that they had not undertaken recent anaerobic exercise the user would be prompted to assess for DKA by means of blood ketone or urine ketone measurement (1418). When using some example test devices, such as those discussed below in relation to
DKA is considerably more common and can be less severe than MALA, and so in the event that ketones are detected, a DKA episode would be assessed. This condition could be managed accordingly (1420) by, for example, following sick day rules and seeking an appropriate level of medical intervention in a timely fashion. Upon successful resolution of the DKA episode, metformin therapy could be resumed (1422).
In the absence of ketones being detected (1424) then an indication may be provided that the user is at risk of sepsis or ischemia. The indication may be provided in response to the user inputting evidence or symptoms consistent with these conditions when prompted to do so. If a sepsis or ischemia related acidosis is assessed, then the user could be prompted to seek appropriate treatment and management accordingly (1426) prior to resuming any Metformin based or other biguanide based treatment (1428).
In the further absence of sepsis or ischemia systems, biguanide based acidosis is suspected (1430). The user is prompted to identify appropriate symptoms and their severity (1430) and the user instigates a hiatus in the Metformin or other biquanide-based therapy (1414). In the event that symptoms were severe, haemodialysis in the Emergency Room is recommended (1432) in an appropriate and timely fashion. The user's kidney functions are checked (1436) before resuming Metformin or other biguanide-based medication. In the event that MALA onset was mild or caught early and that levels showed signs of normalisation after the cessation of biguanide therapy (1434), then severe MALA and hospitalisation could be avoided altogether, and the user could be prompted to seek kidney function tests in a primary healthcare setting (1436) which would establish whether biguanide therapy was still appropriate for them, before it was resumed.
The electrochemical test strip 1500 of
In this example, the first working electrode 1514 is provided with sensing chemistry 1530 for detecting an acidosis-related analyte such as the ketone body β-hydroxybutyrate. The second working electrode 1516 is provided with sensing chemistry 1532 for detecting a second analyte, such as glucose. The third working electrode 1520 is provided with sensing chemistry 1534 suitable for detecting an acidosis-related analyte such as lactate.
Any of the reagent layers 1532, 1534, 1536 may comprise an electron transfer agent, or mediator. In an example, reagent layer 1530 comprises an electron transfer agent having a low standard redox potential such as ruthenium pentaammine chloride or ruthenium hexaammine trichloride. Reagent layers 1534 and 1536 may comprise an electron transfer agent such as potassium ferricyanide.
The reagent layers may comprise any suitable reagents for detecting the respective analytes for each of the working electrodes. For detecting a ketone body such as β-hydroxybutyrate, sensing chemistry 1530 for first working electrode 1514 may comprise β-hydroxybutyrate dehydrogenase, a cofactor, and a diaphorase. For detecting glucose, sensing chemistry 1532 for second working electrode 1516 may comprise glucose oxidase. For detecting lactate, sensing chemistry 1534 for third working electrode 1520 may comprise lactate oxidase.
In use, a fluid sample is provided to the electrochemical test device and a potential difference is applied across the fluid sample to generate a detectable output signal indicative of one or more analyte concentrations in the fluid sample. In this example, in use a blood sample is applied to the sample introduction channel 1538 of the electrochemical test strip 1500. Through capillary action, the blood is drawn into the sample introduction channel 1538 to the electrodes 1514, 1516, 1518, 1520, and 1522 of the conductor layer 1512. That is, the sample introduction channel 1538 acts as a capillary channel. A potential difference is applied across the electrodes 1514 and 1518 and the blood sample, and the electrodes 1518 and 1516 and the blood sample, and the electrodes 1520 and 1516 and the blood sample, and output signals such as transient currents are generated from the blood sample. The characteristics of the output signal(s) can be used to determine the concentrations of one or more analytes.
Any embodiments where both lactate and β-hydroxybutyrate measurements are effected simultaneously enable more ready and immediate disambiguation of the acidosis type using appropriate modifications of the logic already described.
Also, because lactate is often also present in cases of ketoacidosis, and the rarer lactic acidosis is likely to be the underlying cause and condition in circumstances where ketones are absent and only lactate is present, lactic acidosis is more likely to be correctly identified as the “condition indicated” within these tri-analyte systems.
Since ˜68% of DKA episodes include some concomitant lactate elevation, the combined lactate/ketone result from the tri-analyte system can be used to better assess the severity and appropriate management of any ketoacidosis present (where ketones are detected and lactate is present or absent).
For example in circumstances where ketone results were normalising but lactate was continuing to trend upwards, a DKA management regimen or sick day rules that might have otherwise been incorrectly abandoned prematurely would be persisted with by the user, such that acute DKA management was only ended when all 3 levels (glucose, lactate, ketone) had been restored to acceptable levels.
In another example, a DKA episode with a moderate ketone level of e.g. 1 mmol/L with an elevated lactate of e.g. 8 mmol/L that may have been assessed as minor or moderate in the case of glucose and ketone data alone (and therefore appropriate for self-management), could be more appropriately elevated to ‘severe DKA risk’ within the tri-analyte system, once the highly elevated lactate result was factored in along with the ketone and glucose readings. Thus leading to an appropriate and timely health care intervention that could otherwise have been in appropriately delayed.
For example, the severity of an acidosis event could be more appropriately determined by the aggregate (or a suitable weighted aggregate) of the combined analytes above their respective CT1 threshold values, instead of solely on the basis of a single analyte above its individual CT1 threshold value.
In
As the lactate level is above a threshold, the user is asked to input whether or not they have recently been exercising hard, as this may be an indication that a high lactate measurement is due to anaerobic exercise (see discussion above in relation to
A user-selectable option to return to the previous screen is provided. A further option to proceed to a fourth screen (
Variations of the described embodiments are envisaged, for example, the features of all the disclosed embodiments may be combined in any way.
For example, an electrochemical test device may contain more layers than those disclosed in the preceding description. For example, an electrochemical test device may further comprise one or more bonding layers for bonding together one or more of the layers disclosed above. Additionally, some of the layers are not always necessary. For example, the insulator layer may be absent from the examples discussed above. The spacer layer may define the interaction area of the electrodes of the conductor layer beneath. The spacer layer may perform the dual role of receiving a fluid sample through a capillary channel and defining an interaction area for combining the fluid sample with the conductor layer. For example, the spacer layer can, with appropriate adhesive, define the active area/interaction area of the electrodes.
In the examples of the electrochemical test device discussed above, a layer structure has been shown. The order in which each of the layers is formed may vary and any layer may, in some way, be configured so as to be in contact with any other layer.
The present disclosure is equally applicable to a glucose, ketone, lactate (“GKL”) test strip. That is, in embodiments, there are provided three electrodes, one for each analyte.
The fluid sample may be a biological fluid. For example, the biological fluid may be blood, interstitial fluid, plasma, sweat, urine, lachrymal fluid, saliva or breath condensate. The one or more analytes may be any analyte(s) found in the fluid sample. For example, the analytes may be glucose and one or more of lactate, a ketone body such as β-hydroxybutyrate, bicarbonate, pH, or a kidney function analyte. Other ketone bodies that may be detected include acetoactetate, acetone, β-hydroxy pentanoate, and β-keto pentanoate.
The electrochemical test device may be configured to detect any combination of analytes so long as a suitable sensing chemistry is used. Example combinations include glucose and β-hydroxybutyrate; glucose and lactate; and lactate and β-hydroxybutyrate to name a few. Further working electrodes may be provided allowing higher numbers of analytes to be measured. For example, the electrochemical test strip may be configured to detect glucose, lactate and β-hydroxybutyrate.
The electrochemical test device may be any suitable electrochemical test device. The electrochemical test device may be a test strip. In some examples the electrochemical test device may comprise a patch. Electrochemical test devices such as patches typically comprise a subcutaneous fluid extraction set and sensing chemistry for interaction with the one or more analytes. The electrochemical test device may be a monitoring component which transmits an output signal to a separate device such as a meter, either wirelessly or through a wired connection. The electrochemical test device may comprise a continuous monitoring device or a semi-continuous monitoring device.
In the examples discussed above in relation to
The electrochemical test device may be suitable for measuring any fluid sample volume and may be of a suitable corresponding size for the volume. For example the electrochemical test devices described in relation to
Although in the discussion above in relation to
In examples, the device is a layered device. In examples, the first working electrode, second working electrode and, optionally, third working electrode are disposed on one layer of the test device.
In the examples provided above, the conductor layer and the insulator layer are printed layers. The conductor layer and the insulator layer may be supplied using any suitable manufacturing technique. These include forms of printing, for example, screen printing, lithographic printing or tomographic printing. The conductor layer and the insulator layer need not be provided in the same way. Other suitable manufacturing techniques include etching, and/or sputtering, chemical vapour deposition or physical vapour deposition.
A conductor layer may be formed of any suitable conductor. For example, the conductor layer may be formed from a carbon based paste, such as a carbon/graphite paste, including graphene. The conductor layer may be formed of one or more metal based paste such as a gold, platinum or silver paste. Although the conductor layer 112 described above in relation to
The conductor layer may be of any suitable thickness. For example, the conductor layer may have a thickness greater than or equal to 0.005 mm and less than or equal to 0.030 mm.
The ordering of the electrodes on the electrochemical test device may be altered for efficiency. In one preferable option, an electrode for an analyte for which a weak signal is expected (for example β-hydroxybutyrate which is often present in very low concentrations in blood) may be positioned closer to the entrance of the sample introduction chamber than an electrode for an analyte such as glucose or lactate which is usually present in higher concentrations.
The insulator layer may be formed of any suitable insulating material. For example, dielectric/insulation inks may be polymer loaded inks that are thermoplastic, thermoset or UV cured and that, when dried or cured, form a contiguous non-conductive layer. Examples include, Loctite EDAG PF 021 E&C and DuPont 5018.
In the examples discussed above, a polyester substrate layer was featured. Suitable substrate materials include polyester, polyimide, polystyrene, PVC, polycarbonate, glass and ceramic. When other layers are to be printed onto the substrate layer, the substrate layer has to be suitably printable for the chosen inks. The substrate must also be non-conductive. Typical thicknesses of the substrate layer range from 0.1 mm to 0.5 mm e.g. 0.35 mm. Glass and ceramic can be thicker as these are easier to handle with increased thickness. Thinner polymer substrates may be more difficult for the end user to use. Thicker substrates may offer some handling benefits.
The spacer layer may be formed of any suitable material. For example, the spacer layer may be made from a polyester core with a thin layer of PSA (Pressure Sensitive Adhesive) on either side. These adhesives can be the same or different depending on which layer is to be adhered to which side of the spacer layer.
Although in the examples above the thickness of the spacer layer was 0.1 mm, the thickness may vary. A typical range for the spacer layer thickness is 0.005-0.030 mm. Lower thicknesses may affect sensor performance and higher thicknesses would increase the volume of the sample introduction channel. A thickness of an adhesive on the spacer layer may contribute to the rigidity of the spacer layer.
Typically a spacer layer has a high volume resistivity. For example the volume resistivity may be greater than 1×109 Ωcm.
Other variations of the spacer layer are envisaged.
The sample introduction chamber may be provided along the longitudinal axis of the electrochemical device. The sample introduction chamber may be provided along the transverse axis of the electrochemical test device.
The vent may be of any suitable configuration for venting air from the sample introduction chamber. For example, the vent may comprise an air passageway in the cover. The vent may comprise an air passageway in the spacer layer. Optionally, air may be vented from the sample introduction chamber through one or more air passageways below the spacer layer, such as through the conductor layer or the insulator layer.
In the examples above, the sensing chemistry is applied to each of the working electrodes as two reagent layers. There may be more than two reagent layers. For example, there may be a number of intermediate layers between a layer adjacent the electrode and a layer for coming into contact with the fluid. There may only be one reagent layer on a working electrode.
Many electron transfer agents or mediators may be used with electrochemical test devices such as those described herein. For example, suitable mediators include quinones such as benzoquinone, dyes such as 2,6-dichlorophenolindophenol and tetrazolium dyes, and redox couples such as ferricyanide anions and ferricinium cations, phenazine ethosulfate, phenazine methosulfate, 2-methyl-1,4-naphthoquinone and ferrocene derivatives.
The electron transfer agent may comprise a suitable quinone, for example a naphthoquinone derivative. The naphthoquinone derivative may be a 1,2 naphthoquinone derivative or a 1,4 naphthoquinone derivative. For example, the electron transfer agent may comprise 1,4 naphthoquinone-2-mercapto methyl carboxylic acid which has a standard redox potential of around −0.355V. The electron transfer agent may comprise 1,4 naphthoquinone-2-mercapto benzoic acid, which has a standard redox potential of around −0.345V. The electron transfer agent may comprise 1,2 naphthoquinone-4-sulphonate, which has a standard redox potential of around −0.214V. The electron transfer agent may comprise 1,4 naphthoquinone-2-mercapto methyl sulphonate. Also other suitable isomers of the above listed compounds are known which have similarly low standard redox potentials.
Both ruthenium hexaammine trichloride and ruthenium pentaammine chloride were mentioned above as suitable mediators. Other ruthenium-based complexes that may be used as a mediator include ruthenium pentaammine 4-methyl pyridine and ruthenium pentaammine pyridine.
The electron transfer agent may be a ruthenium- or osmium-based electron transfer agent. The ruthenium- or osmium-based electron transfer agent may be a complex of formula (3),
[M(A)x(B)y](X)n (3)
wherein M is ruthenium or osmium, A is an amine ligand, each B is a ligand different to A, x is an integer selected from 1 to 5, y is an integer selected from 1 to 5, x+y is 6 or 8, n is an integer selected from 1 to 6, and X is any suitable counterion.
M may be ruthenium. For example, M may be Ru(II) or Ru(III). The oxidation state of the metal M in the complex may be selected to be 2+, 3+ or 4+.
A may be NRR′R″, wherein R, R′ and R″ are independently selected from hydrogen or alkyl. A may be NH3. It will be appreciated that when x is two or more, all “A” may be the same.
Each B is a ligand different to A. It will be appreciated that when y is 2 or more, B may be the same or different. B may be independently selected from a halide or optionally substituted heteroaryl. When B is an optionally substituted heteroaryl, the heteroaryl may be optionally substituted with an optionally substituted C1-6 alkyl. B may be a halide, and the halide may be selected from the group consisting of F−, Cl−, Br−, I−. B may be chloride. B may be pyridyl, or 4-methyl pyridyl.
It will be appreciated that A and B may be selected such that the overall charge on the complex of formula (1) is selected from the group +2, +1, 0, −1, −2 and −3.
The counterion X may be a counterion selected to lead to the charge neutrality of [M(A)x(B)y]. The counterion X may be selected from F−, Cl−, Br−, I−, PF6−.
The ruthenium complex may be [RutheniumIII(NH3)5(pyridine)]X. The ruthenium complex may be [RutheniumIII(NH3)5(4-methyl pyridine)]X. The ruthenium complex may be [RutheniumIII(NH3)5Cl]X (ruthenium pentaammine chloride). The ruthenium complex may be [RutheniumIII(NH3)5Cl].2Cl.
The counterion X may be a counterion selected to lead to the charge neutrality of [M(A)x(B)y]. The counterion X may be selected from F−, Cl−, Br−, I−, PF6−.
The ruthenium- or osmium-based electron agent may be a ruthenium-based electron transfer agent. The concentration of the ruthenium-based electron transfer agent in the sensing chemistry may be from 8% to 15% by weight before drying of the sensing chemistry.
Transition metal complexes of the present disclosure can be soluble in water or other aqueous solutions. In general, the transition metal complexes can be made soluble in aqueous solvents by having an appropriate counterion or ions, X. The solubility of the transition metal complex may be greater than about 0.025M at 25° C. in water.
Suitable electron transfer agents may be osmium-based compounds. For example, osmium phendione may be used as a mediator. [Os(4,4′-dimethyl-2,2′-bipyridine)2] may also be used as a mediator, as may [(trpy)(bpy)M-OH]2+ (M=Os; trpy=2,2′,2″-terpyridine; bpy-2,2′-bipyridine).
The sensing chemistry may comprise between about 0.3%-2% (w/w) diaphorase. The sensing chemistry may comprise about 1% (w/w) diaphorase.
The diaphorase may be dissolved in a buffer such as, for example, phosphate or citrate. The buffer may be Tris buffer. The pH of the buffer may be about 7.
The sensing chemistry may comprise a phosphate or Tris buffer. The pH of the buffer may be in the range of about 6.5-7.5. For example, the pH of the buffer may be about 7. The pH of the buffer may be in the range of about 9.5-11. For example, the pH of the buffer may be about 10.5. The buffer may be of any suitable pH.
The diaphorase may have an enzyme activity range of from about 75 kU to 200 kU per 100 grams composition. The enzyme activity range is selected so that the analyte current does not depend on the level of enzyme activity in the composition and to avoid solubility issues for too high levels of diaphorase.
The sensing chemistry may comprise between about 0.07%-0.13% (w/w) flavin mononucleotide (FMN). The sensing chemistry may comprise 0.1% (w/w) FMN.
The sensing chemistry may comprise about 0.5%-3.5% (w/w), or 2.5%-3.5% (w/w), hydroxyethyl cellulose (HEC). The sensing chemistry may comprise 3% HEC.
In the context used herein, “about” may refer to a variation of ±10% of the numerical value.
A reagent for reacting with an analyte in a fluid sample need not be an oxidase. For example, for detecting glucose, rather than a glucose oxidase the sensing chemistry of a working electrode may comprise a dehydrogenase, such as flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase with its FAD cofactor, or pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase with its PQQ cofactor. Alternatively, a NAD(P)+-dependent dehydrogenase such as NAD(P)+-glucose dehydrogenase may be used. For example, for detecting lactate, rather than a lactate oxidase the sensing chemistry of a working electrode may comprise a dehydrogenase, such as a lactate dehydrogenase.
Whilst the above examples have been described primarily in the context of an electrochemical test device for measuring a concentration of an analyte in a bodily fluid, it may equally be used in other fields, for example in health and fitness, food, drink, bio-security applications and environmental sample monitoring. The examples described herein may equally be used in the context of animal/veterinary medicine and fitness (including dogs and horses).
The apparatus may be configured to receive one or more test devices in order to receive information for determining concentrations of measured analytes. Information received may be time-stamped so as to check for sample relevance. Information may be received from other analytical equipment.
The above embodiments have been described by way of example only, and the described embodiments are to be considered in all respects only as illustrative and not restrictive. It will be appreciated that variations of the described embodiments may be made without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1510765.9 | Jun 2015 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2016/051829 | 6/17/2016 | WO | 00 |
