Patent Application
20100190193
The present invention is directed to diagnostic compositions for use in the viscoelastic analysis of a test liquid, and to a container comprising same. The present invention further is directed to a method of performing a viscoelastic analysis on a test liquid, and to the use of the diagnostic composition in such a method.
The coagulation of blood is a complex process during which blood forms solid clots. It is an important part of hemostasis (the cessation of blood loss from a damaged vessel) whereby a damaged blood vessel wall is covered by a blood clot to stop hemorrhage and aid repair of the damaged vessel. Disorders in coagulation can lead to increased hemorrhage and/or thrombosis and embolism.
In a normal individual, coagulation is initiated within 20 seconds after an injury occurs to the blood vessel damaging the endothelial cells. Platelets immediately form a haemostatic plug at the site of injury. This process is called primary haemostasis. Secondary haemostasis follows if plasma components called coagulation factors respond in a complex cascade to form fibrin strands which strengthen the platelet plug.
The coagulation cascade of secondary hemostasis has two pathways, the Contact Activation pathway (formerly known as the Intrinsic Pathway) and the Tissue Factor pathway (formerly known as the Extrinsic pathway) that lead to fibrin formation. It was previously thought that the coagulation cascade consisted of two pathways of equal importance joined to a common pathway. It is now known that the primary pathway for the initiation of blood coagulation is the Tissue Factor pathway. The pathways are a series of reactions, in which a zymogen of a serine protease and its glycoprotein co-factor are activated to become active components that then catalyze the next reaction in the cascade. Coagulation factors are generally indicated by Roman numerals from I-XIII, with a lowercase ‘a’ appended to indicate the activated form.
Fibrinolysis is the process where the fibrin clot is broken down. Tissue plasminogen activator (tPA) and urokinase are the agents that convert plasminogen to active plasmin, thus allowing fibrinolysis to occur.
The detection of normal or decreased functionality of these coagulation components is important in order to assess patients' hemostasis disorders.
Several methods of measuring the coagulation characteristics of blood are known. Some such devices attempt to simulate the natural flow of blood in the veins and arteries of a living subject, while other measurement techniques are performed in static blood volumes.
An accurate measurement of the ability of a patient's blood to coagulate in a timely and effective fashion is crucial to certain surgical and medical procedures. Rapid and accurate detection of abnormal coagulations is also of particular importance with respect to appropriate treatment to be given to patients suffering from clotting disorders. Often the condition of such patients makes it necessary to administer blood components, anti-coagulants, certain fibrinolytic agents, anti-platelet agents, or compounds inducing the reverse effects of said agents. In these cases, the treatment dose can be adapted to the extent of a clotting disorder previously determined.
Measurements of blood clotting are provided by various devices, for example as disclosed in (U.S. Pat. No. 5,777,215), (U.S. Pat. No. 6,537,819), or (U.S. Pat. No. 5,777,215). These devices measure the mechanical properties of the clot throughout its structural development. These systems are summarized under the term “viscoelastic methods”, as they continuously detect viscoelastic properties of the blood clot while its formation and lysis.
A viscoelastic measurement provides information about several distinct parameters, for example the time between coagulation activation and clot initiation (clotting time CT), the dynamics of clot formation (clot formation time CFT), the firmness of the clot (amplitudes A5-A30 and maximum clot firmness MCF), or the extent of fibrinolysis (maximum lysis ML).
A number of references describe instruments for measuring blood clotting characteristics based upon mechanical movements. These instruments monitor the elastic properties of blood as it is induced to clot under a low shear environment, i.e. in static blood volumes. The patterns of change in shear elasticity enable the determination of the kinetics of clot formation, as well as the strength and stability of the formed clot. The strength and stability of the clot provide information about the ability of the clot to perform the “work of hemostasis” (i.e., stop or prevent abnormal bleeding) and about the adequacy of blood platelet-fibrin interaction. The kinetics of clot formation mainly provides information about the functionality of coagulation factors. Analysis of all of this information provides results which are useful to predict bleeding, to monitor and manage thrombosis, or to monitor fibrinolysis.
However, as the clotting process consists of various interlinked components, the use of specific activators and inhibitors is further applied in order to detect hemostasis disorders more specifically.
Accordingly, the reagents used in viscoelastic analysis consist of an initial activator (e.g., an activator of either the intrinsic or the extrinsic pathway) and optionally one or more inhibitors (e.g., fibrinolysis inhibitors, heparin inhibitors, platelet inhibitors) and/or one or more further specific factor of the coagulation cascade.
Optionally further components may be added:
Depending on the diagnostic aim, these reagents can be used either alone or in combination: For example, a measurement with only intrinsic activator in the sample can be combined with a measurement with intrinsic activator and a sufficient amount of heparin inhibitor (e.g., heparinase) in the sample to detect the presence of heparin in the test liquid; a combination of extrinsic activator and platelet inhibitor (e.g., Cytochalasin D) in the sample is applied to determine the activity of fibrinogen without platelet contribution in the test liquid.
There is a reagent concept for viscoelastic measurements in the literature (ReoPro-modified TEG: Wenker et al.: Thrombelastography, The Internet Journal of Anesthesiology, 2000, Volume 1 Number 3; (http://www.ispub.com/ostia/index.php ?xmlFilePath=journals/ija/volln3/teg.xml); Ruttmann et al.: Hemodilution Enhanced Coagulation Is Not Due to Platelet Clumping, Anesthesiology 2004; 101: A150; Recombiplastin- and ReoPro-modified TEG:http://www.transfusionguidelines.org.uk/docs/pdfs/bbt_app-use_teg-sop-example.pdf; TF- and Trasylol-modified TEG: Tanaka et al.: Evaluation of a novel kallikrein inhibitor on hemostatic activation in vitro, Thrombosis Research, Volume 113, Issue 5 , 2004, Pages 333-339) that is based on the combination of commercially available activator reagents intended for other tests, such as the prothrombin time activator Innovin or Recombiplastin®, combined with customer-made CaCl2 solution and drugs, such as ReoPro® (abciximab) and Trasylol® (aprotinin). This leads to a low standardization, many pipetting steps and many sources of error.
There is a reagent system for viscoelastic measurements marketed by Pentapharm, which is based on standardized reagents, most of which are provided to the customer in a liquid form, which are pipetted by the user into the test cup using standardized operating procedures. This standardizes the application; however it still requires several pipetting steps for the analysis. For example, to perform a FIBTEM test together with an EXTEM control test, the pipetting of blood, CaCl2 solution, extrinsic activator and a platelet inhibitor may result in the performance of a total of 8 pipetting steps (including three times changing of the tip during one test procedure) and the need for 3 different reagents that have to be handled by the user. This provides a requirement for training consumes time and is a potential source of error.
There are other reagent systems on the market, which are based on a variety of reagents. Some of them are liquid, and have to be pipetted into the cup (e.g. CaCl2 solution), some are dried into the test cup (such as heparinase) and some are provided in small vials, in a quantity intended for one test. A characteristic of these reagents is that still each reagent is typically provided alone, and therefore several steps are required at least for tests requiring more than one active reagent.
Accordingly, some efforts have been done in the past to provide a simpler reagent system for viscoelastic measurements of blood or blood components:
One shortcoming of the strategy of drying active reagents directly into the test cup is that these are typically made of plastic and are light, which makes the filling of these cups in automated reagent dispensing lines more difficult. This makes manual filling steps necessary or the development of specialized equipment, which are both costly.
Another shortcoming of this strategy is that the active components or stabilizers may interfere with the adhesion strength of the blood clot on the cup surfaces, which is required to perform correct measurements. For example, there has been shown diminished clot adhesion after incubation of albumin solution into the cup (Albumin is a typical stabilizer used to stabilize all kinds of proteins in reagents):
Another possible strategy to simplify the handling of the reagents is to combine the different reagents necessary for one test in liquid phase in their working concentration. The main problem here is the interaction of the different substances while staying together for a longer period. Some components negatively affect the stability of each other when staying together in the liquid phase at higher concentrations; for example, CaCl2 disturbs the stability of Tissue Factor reagent in liquid phase over the time.
Moreover, if these combined reagents should be provided in an amount sufficient for exactly one test, another problem would arise: In this case, the very small portion of liquid reagent might stick to parts of the reagent container or the cap and might thus not mix sufficiently with the test liquid when the analysis is performed.
One strategy proposed to solve the named aspects was disclosed by Kolde et al. in US patent application 20040071604. In this application, a cup system for viscoelastic analyses is presented, in which the lower end of the cup is divided in several reagent chambers. This allows to place the reagents independently into the different chambers, without mixing them and then to freeze-dry the reagents.
However, disadvantages of this solution include the need for a very precise pipetting process, as the separate reagent chambers are very small and also the problem that the reagent drops might still mix before the freeze-drying by vibrations present on the reagent filling line. Another problem is the possible air-drying of the small reagent drops during the processing under room conditions before the lyophilisation process starts. Again the problem of automatically handling the small plastic and thus very light using standard reagent-filling lines is present.
The most coagulation test methods in routine lab use just measure the time from adding an activator to the sample until the first initial formation of a fibrin clot can be detected (=clotting time). They stop at this point and no further measurement is done. This has the implications, that in these methods a firm adhesion of the blood to the surfaces of the measurement cell is not necessary. Accordingly, the variety of analyzers and reagents available for the assessment of clotting times with such methods does not have to handle the unique problems connected with viscoelastic measurements.
Therefore, it is an object of the present invention to provide a diagnostic composition, which allows for a safe, reproducible and easy to use procedure for different tests in viscoelastic systems. It is a further object of the present invention to provide a diagnostic composition which is specifically adapted to one single analysis of a blood sample and has a superior reagent stability regarding prior art compositions. It is a still further object of the present invention to provide a diagnostic method which provides reliable and reproducible results, is easy to handle and which provides a standardized system for the determination of the coagulation characteristics of a blood sample.
These objects are attained by the diagnostic composition of claim 1, the container of claim 15, the diagnostic method of claim 18 and the use of claim 26.
Preferred embodiments are set forth in the dependent claims.
By using the diagnostic composition of the invention, the tests may be performed as follows: a defined volume of a sample (e.g., whole blood, blood plasma etc.) is added directly into a container 1 containing the diagnostic composition. After dissolving of the composition in the blood sample, the resulting mixture is pipetted from the container 1 into the measuring cup 2 of a measuring apparatus 4. The cup 2 is then put into a position such that the pin 3 is immersed into the liquid in the test cup (cp.
Therefore, the user needs only 4 pipetting steps for each test to perform (in the prior art liquid system up to 8 steps, see above) and no change of the pipette tip is necessary.
Thus, it is clear that the present system for the determination of coagulation characteristics of a blood sample can be handled easier, thereby making the likelihood of errors smaller, which can be due to an imprecise line of action by a (potentially less experienced) operator.
Therefrom, further advantages may arise as, for example, a higher reproducibility of the results to be achieved, and thus, a higher degree of standardization.
Furthermore, one advantage of the present approach is that the diagnostic composition (i.e. reagent mixture) of the invention may be provided in a larger volume (and thus in a lower concentration) prior to the step of lyophilization than it is present in the final measuring step. In more detail, it is advantageous to initially provide a low concentration of the reagent mixture in order to avoid an early reaction of the reagents. The final concentration in the measuring step (obtained by resolving the diagnostic composition in the test sample) then will be higher than the initial concentration present before the lyophilization step.
Further features and advantages of the present invention will be evident from a description of embodiments with reference to the figures.
In the figures:
In a first aspect, the present invention provides a diagnostic composition for use in the viscoelastic analysis of a test liquid, comprising the following constituents:
The calcium salt preferably is CaCl2.
The diagnostic composition or reaction mixture of the present invention comprises constituents, which are per se known in the art. One difference to the prior art approaches is, however, that the mixture of these constituents is provided in an essentially dry form.
“Essentially” dry in the context of the invention means a state, wherein the mixture is essentially free from any liquid or moisture, in particular being depleted of water. Water or any other liquid, however, may be present as residue in the mixture, but only to an extent, which does not negatively influence the stability of the overall composition. In particular, it has to be excluded that an interaction occurs between the different constituents, which negatively affects the stability. A remaining amount of liquid, preferably water, in the composition of up to 10% by weight should be acceptable.
The amount sufficient for performing one single viscoelastic analysis of a specified test liquid, for example a blood sample, is that amount of all constituents in mixture, which provides the required concentration of the reagents in the final analysis of the coagulation characteristics of the blood sample, i.e. in the cup 2 of a measuring apparatus 4. Therefore, it is not necessary to further portion the diagnostic composition before or after dissolving it in a liquid.
Further, this is achieved by dissolving the substances in the test liquid (blood sample etc.) itself, not by dissolving the constituents in an amount of liquid diluent leading to the final working concentration.
The activator of coagulation as mentioned above preferably is an intrinsic and/or extrinsic activator.
The extrinsic activator of coagulation in turn preferably is the Tissue Factor (TF) and is more preferably selected from lipidated TF or rTF.
The intrinsic activator of coagulation is preferably selected from celite, ellagic acid, sulfatit, kaolin, silica, RNA, or mixtures thereof.
As a second feature, the diagnostic composition of the present invention may optionally comprise a calcium salt such as CaCl2, wherein CaCl2 is preferably present in an amount of about 1-100 μmol/ml of test liquid. As mentioned above, the amount of CaCl2 must be sufficient to ensure recalcification of the test liquid, in particular of the blood sample, if the sample was decalcified before. It turned out that the amount of from 3-30 μmol/ml is optimal to achieve this requirement. In order to determine the required amount of CaCl2 to be contained in the diagnostic composition even more precisely, the exact volume of the test liquid to be collected from the patient has to be known as well as the amount of decalcifying reagent employed.
The diagnostic composition of the present invention optionally contains one ore more inhibitors, being selected, for example, from one or more of a platelet inhibitor, fibrinolysis inhibitor, or heparin inhibitor.
Those inhibitors may be used and combined depending on the precise diagnostic demands, for example, the platelet inhibitor may be a cyto-skeletton inhibitor or a GPIIb/IIIa antagonist. The like, the fibrinolysis inhibitor can be selected, for example, from aprotinine, tranexamic acid, or eaca; the heparin inhibitor might be selected, for example, from heparinase, protamine or protamine-related peptides; and the coagulation factor can be selected, for example, from one or more coagulation factors or activated coagulation factors preferably FXa or FVa or activated protein C or FVIIa. However, it is noted that this is only a preferred selection and further inhibitors can be used if required.
In a preferred embodiment, the dry mixture is a lyophilized mixture, more preferably a mixture produced by co-lyophilization of a mixture of the liquid reagents in one single lyophilizytion process. More precisely, in this preferred embodiment the diagnostic composition is produced by filling liquid components—in the required quantities to reach the intended composition—into a suitable container 1 (for example by a pipetting machine) and drying this composition in the container 1 under application of low pressure environment (about 1000-0.2 mbar) at suitable temperature (about +30° C. to −70° C.). The container 1 then may be closed or sealed by a close cover or the like (e.g., a lid 5) in order to avoid a loss of reagents, or an invasion of contaminants, water etc.
In a preferred embodiment, the diagnostic composition may also contain one or more stabilizers, wherein the stabilizer preferably is albumin or gelatine.
In a preferred embodiment, the diagnostic composition may also contain one or more phospholipids, wherein the phospholipids may be a composition of different phospholipids like phosphatidyserine, phosphatidylethanolamine and phosphatidylethanolcholine. For example, mixtures of phospholipids extracted from rabbit brain may be used.
The present diagnostic composition may have the following constitution in preferred embodiments:
In a second aspect, the present invention provides a container 1, comprising the diagnostic composition as defined above. The container 1 preferably takes the form of a vial or a cuvette.
The container 1 is formed from a material (e.g., plastic or glass) which is not corroded or otherwise affected by the reagents to be filled in or the test liquid to be filled in.
The container 1 may have cylindrical shape, but its shape does not necessarily have to be cylindrical. The container 1 may have a form which reduces its inner lateral profile from the upper opening to the bottom, as for example a conically shaped form as indicated in
Furthermore, such small vials might become harder to manage for common automated processing systems and might thus increase the production costs.
The cross-section of a basically axially symmetric container 1 of a preferred embodiment is shown in
As mentioned above, the container 1 may be closed or sealed by a lid 5 or the like in order to avoid a loss of reagents, or an invasion of contaminants, water etc.
In a further embodiment, the container 1 is designed in a way that it can be directly used as the measuring cup 2 of the viscoelastic measuring apparatus 4. In other words, a viscolelastic analysis can be performed such that a respective container 1 is provided, the test liquid is added into the container 1, and the measurement is performed directly in the container 1. In this case, only the blood dispension into the container has to be performed as a liquid transfer step, which can be realized by using a manual pipette, an automated pipette, an automated dispenser or any other liquid transfer equipment.
In this embodiment, the container 1 might be designed by combination of two materials, e.g., glass and plastic or glass and a surface covering. As indicated in
In these embodiments, possible coagulation activation in the test liquid by the glass surface is excluded, while the superior sealing properties of the glass material when compared to plastic material are still used. The similar effect of suppressing possible coagulation activation in the test liquid by the glass surface can be realized by covering the glass surface (or at least the inner portion of the glass surface) with a layer of one or more substances that are not able to activate coagulation if they are in contact with blood or blood components.
For comparison, a prior art measuring cup 2 according to US 2004/0071604 is illustrated in
A container 1 is provided, which serves as reagent support and measuring vessel (i.e. can be regarded as a measuring cup 2) for analysis using various analytical processes, and has a region which is divided into at least two chambers (6a, 6b, 6c) by one or more bars extending from the container wall or the container base, wherein the chambers are arranged so that liquid or solid reagents may be introduced therein without them being able to be mixed by diffusion or running into one another. The container 1 is used for drying or freeze-drying by with completely or partly filled chambers and serves at the same time as a measuring vessel after re-dissolving the dried material by adding water, reagent solution, or the sample present in aqueous phase.
Hence, the main difference of the present invention when compared to prior art in US 2004/0071604 is provided by the co-lyphylization process of a mixture of reagents in the cup. This makes the division of the vessel into two or more regions—separated by bars—unnecessary, thus avoiding the resulting complications for the production process by filling in at least two different liquids into two different portions of the vessel.
In a third aspect, the present invention is directed to a method of performing a viscoelastic analysis on a test liquid, preferably a blood sample, comprising the steps of:
As already mentioned above, the test liquid preferably is a blood sample, preferably is a mammalian, more preferably a sample of human blood or blood components (e.g., whole blood or blood plasma).
Step c) of the method of the present invention preferably takes about 1-60, more preferably 2-10 sec and most preferred is about 5 sec. Following that time, the mixture of the diagnostic composition and the blood sample should be quickly transferred to the measuring cup 2 of the measuring apparatus 4. This is done in step d) by manually or automatically pipetting the mixture from the container 1 and by transferring it thereby to the apparatus 4, i.e. to the measuring cup 2 of the apparatus 4.
As an alternative, if the container 1 of the present invention is the measuring cup 2, the measurement is performed directly in the container 1. In this case, step d) may be omitted.
The apparatus 4 preferably is a device suited for viscoelastic measurements, for example devices disclosed in (U.S. Pat. No. 5,777,215), (U.S. Pat. No. 6,537,819), or (U.S. Pat. No. 5,777,215).
One example of that apparatus 4 is shown in
After the formation of the clot between cup 2 (cuvette) and pin 3, the clot itself is stretched by the movement of the pin 3 relative to the cup 2. The detection of the characteristic parameters of the clot is based on the mechanical coupling of cup 2 and pin 3 by the clot. This is only possible if the clot adheres on the surfaces of both cup 2 and pin 3. So, a firm adhesion on the surfaces of both cup 2 and pin 3 is essentially required for the viscoelastic analysis.
The method of the present invention comprises such a viscoelastic analysis of a blood sample in order to determine its coagulation characteristics, wherein such a viscoelastic analysis in the broadest sense is the measurement of a relative movement of a cuvette containing a blood sample relative to a punch. The analysis preferably comprises the determination of the clotting time, the clot formation time, and the firmness of the clot over time including fibrinolytic effects.
In practice, the following steps may be performed:
Therefore, the user needs not more than 4 pipetting steps in total for each test to perform (compared to the up to 8 steps required for a liquid reagent system) and no change of pipette tip is necessary when preparing one test. This clearly indicates the direct benefit of the present invention for the person who is performing such tests.
In a further aspect, the present invention is directed to the use of a diagnostic composition or a container 1 as defined above in a method for analyzing the viscoelastic behaviour of a test liquid, preferably a blood sample.
Although the present invention has been described in accordance with preferred embodiments, it is obvious for a person skilled in the art that modifications are possible in all embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0701821.1 | Feb 2007 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB08/00208 | 1/31/2008 | WO | 00 | 3/10/2010 |
