Patent Application
20060062688
1. Field of the Invention
The invention in general relates to bodily fluid analysis systems including a disposable test strip, with particular application to on-site testing of particular analytes in blood.
2. Statement of the Problem
The level of certain analytes in blood and other body fluids is often used to diagnose disease, determine disease risk factors, monitor the course of a therapy, or determine the presence of illicit drugs. In recent years, analytes carried in blood have been evaluated to determine various cholesterol and triglyceride levels as a significant indicator of risk of coronary heart disease. Physicians commonly order what is referred to in the art as a “full lipid panel” for patients to determine the concentration of total cholesterol, high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), and triglycerides.
Clinical chemists prefer to work with blood serum over plasma, and plasma over whole blood, because of the clarity of the sample matrix and the lack of interfering substances from the solid portion of the blood. To facilitate this analysis, a separation step must be carried out since the presence of red blood cells, either intact or hemolyzed, interferes with detection of the signal generated by the chemical reaction performed by the test. Conventionally, the separation of blood components has been carried out by centrifuging a clotted blood sample, and the serum thus obtained is used to carry out the test.
In more recent years, dry test strips have been developed that utilize several layers to separate the blood components, react the plasma with a particular reagent or reagents, and obtain a colorimetric signal indicative of the concentration of the analyte. See, for example, U.S. Pat. No. 5,104,619 entitled “Disposable Diagnostic System”; U.S. Pat. No. 5,166,051 entitled “Membranes, Membrane Overlays, For Exclusion of Erythrocytes, And Method Of Immunoassay of Whole Blood Analytes”; U.S. Pat. No. 4,774,192 entitled “A Dry Reagent Delivery System With Membrane Having Porosity Gradient”; and U.S. Pat. No. 4,477,575 entitled “Process and Composition For Separating Plasma or Serum From Whole Blood”. In more recent systems, the dry test strip is placed within a spectrophotometric device that evaluates the colorimetric response and assigns a quantitative value indicative of the analyte concentration in the blood sample. For example, see U.S. Pat. No. 5,597,532 owned by the assignee of the present invention and entitled “Apparatus For Determining Substances Contained In A Body Fluid”, which patent is incorporated by reference to the same extent as though fully disclosed herein.
All of the above systems depend on flow of the bodily fluid, i.e., blood, through the system as the driving force to separate the unwanted components, e.g., the red blood cells, from the analytes to be tested, e.g., the serum, or, in a system for testing HDL, the other lipoproteins other than HDL. For example, U.S. Pat. No. 4,774,192 relies on a highly porous bottom layer to allow the fluid to flow easily and a dense upper layer to trap the unwanted components. In U.S. Pat. No. 4,477,575, a lateral flow of blood through a fiberglass layer is used to separate the components. U.S. Pat. No. 5,597,532 uses a vertical flow downward through membranes and a lateral flow outward in a lower membrane that is designed to absorb a large amount of fluid to drive the fluid flow. A rectangular test membrane that is significantly larger than the area of the circular opening through which a spectrophotometer reads the strip enhances this feature to encourage flow and prevent blood pooling in the test area of the membrane.
One problem with the test strips of the prior art is that the reagent layer is dosed with a specific mount of reagent based on the anticipated volume of blood sample running through the test strip. If too large a volume of blood is used, reagent that does not react can reconstitute and leach out from the reagent layer. This phenomenon leads to an incorrect color response, and ultimately to an inaccurate reading on the spectrophotometric device. Another problem with the prior dry test strip architectures is that the strips are prone to seepage at the sides of the strip layers. In certain cases, as the blood sample spreads across a strip layer, a certain amount of the sample will seep past the sides of the layer and flow onto the adjacent layer. This cross-contamination can produce erroneous results, especially where the cross-contamination occurs at the reagent layer. Another problem is that the membranes that provide high flow, and thus good separation of the unwanted components from the analytes, such as the asymmetric membranes of U.S. Pat. No. 4,774,192, inherently have low capacity for holding fluid, and thus the problems associated with leaching and seepage are exacerbated.
In addition, test strips of the prior art which have been designed to augment flow have tended to damage the test strip. If the strip is held loosely in the carrier, flow is augmented, but the strip can move, which can lead to erroneous results. Thus, test strip holders have been designed that permit vertical and lateral flow through most of the strip, but tightly hold other parts of the strip. See, for example, U.S. Pat. No. 5,597,532 referenced above. While such holders hold the test strip firmly and at the same time permit flow both vertically and laterally, they can also damage the test strip, which again leads to inaccuracies in measurement.
The conflict between the need for good separation of unwanted components from the analytes, the need to prevent the test strip from moving in the holder, and the problems associated with such flow strip holders, has caused the accuracy of the test strip/spectrophotometric systems to plateau, and has limited the usefulness of this art. Thus, there is a need for a test strip/spectrophotometer architecture that can improve the capabilities of the dry strip technology system and that yield more accurate readings.
The present invention provides a solution to the above problems by providing a strip holder that includes a holder base that forms a well that essentially completely encircles the test strip element, and a cover that uniformly contacts the test strip element about the periphery of the element, with the test strip element secured in the well between the cover and base. In this way, stresses that can damage the strip element are avoided. This also prevents leaching, but at the same time impedes lateral flow except for the initial lateral flow that distributes the fluid across the strip, and thus impedes filtering that the prior art believed was necessary. This has lead to a complete rethinking of how a test strip should operate, as discussed in the following.
The present invention also provides a solution to the above problems in that the dry test strip holder provides a sample container for the test strip element that is essentially closed on the bottom and sides so that it holds a well-defined volume of bodily fluid. The invention recognizes for the first time that in such a closed system the unwanted components do not have to be filtered. It is only necessary to slow the flow of the unwanted components as compared to the flow of the desired analytes. That is, in a closed system, once the sample container is filled, flow stops. Thus, if the reaction layer is placed at the bottom of the container, only the fastest flowing components will reach it before flow stops.
It follows from the above that, instead of filtering the red blood cells, for example, it is sufficient to only slow their progress in the flow. Preferably, the progress of the red blood cells is slowed by using membranes that impede the red blood cells but allow the desired analytes to flow easily. Similarly, it is recognized that precipitated or complexed analytes will not flow as readily as analytes in solution. Thus, for example, for an HDL test, if the non-HDL lipoproteins are precipitated or complexed while the HDL lipoproteins are solubilized, the HDL lipoproteins will flow more easily and reach the reaction membrane at the bottom of the sample container before flow stops. Thus, only the HDL lipoproteins will take part in the reaction.
The invention provides a carrier for a diagnostic test strip for use in measuring analyte in a fluid sample, the carrier comprising: a carrier body having a test opening enabling the test strip to be observed; a test strip well formed around the test opening, the well having an upward sloping well wall completely encircling the test opening, the bottom of the well forming a test strip support; a cover having a sample opening, the cover including an outwardly projecting flange completely encircling the sample opening; and engagement elements on the carrier body and the cover configured to engage the cover to the carrier body with the sample opening aligned over the test opening with the test strip secured between the distal end of the flange and the test strip support. Preferably, the flange and the test strip support are configured so that the test strip will be compressed between the distal end of the flange and the test strip support. Preferably, the test strip support further includes a rounded raised lip between the test opening and the well. Preferably, the distal end of the flange is rounded. Preferably, the curvature of at least a portion of the distal end of the flange corresponds to the curvature of at least a portion of the well wall. Preferably, the test strip well is circular, though it may also be rectangular. Preferably, the test strip well is sufficiently large to completely contain the test strip. Preferably, the carrier body and the cover are configured to completely enclose the test strip except for the test opening and the sample opening. In another embodiment, the test strip well is of a depth so that it can contain only a portion of the test strip. Preferably, the engagement elements include a ramp and a groove forming a snap-fit engagement between the base and the cover.
In another aspect, the invention provides a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the system comprising: a test strip having a test area and containing a reagent capable of interacting with the bodily fluid to determine the characteristic; a test strip holder comprising: a test holder base having a test strip support supporting the test strip and a sensor port communicating with the test strip; a test holder cap having a sample port and a projecting flange; the test holder base and the cap including an engagement mechanism configured to secure the cap to the base with the test strip held between the flange and the test strip support along essentially the entire periphery of the test area. Preferably, the flange is of a length such that when the cap is secured to the test holder base, the distance between the test strip support and the distal end of the flange is less than the uncompressed thickness of the test strip. Preferably, the test strip support includes a lip that defines a recess between the lip and the container wall. Preferably, the engagement mechanism includes a ramp. Preferably, the test holder base includes a plurality of flexible and resilient fingers. Preferably, the cap includes a groove for receiving the fingers. Preferably, the test holder base, the dry test strip, and the cap form a container having a sidewall and bottom and wherein the sidewall and bottom are essentially impervious to liquid. Preferably, the container and the dry test holder are circular. Preferably, the test holder base and the cap, when engaged, completely enclose the test strip except for the ports. Preferably, the cap further comprises one or more welding tabs extending away from the body of the cap. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood.
In a further aspect, the invention provides a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the system comprising: a test strip containing a reagent capable of interacting with the bodily fluid to determine the characteristic; and a test strip holder comprising: a test holder base having a sensor port communicating with the test strip; a test holder cap having a sample port communicating with the test strip, the test holder cap secured to the test holder base with the cap and base completely enclosing the test strip except for the ports. Preferably, the test strip is held between the cap and the base. Preferably, the test strip is compressed between the cap and the base. Preferably, the test strip covers the sensor port and prevents fluid from passing through the sensor port. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood.
In yet a further aspect, the invention provides a method of manufacturing a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the method comprising: providing a base having a sensor port, a cap having a sample port, and a test strip; placing the test strip on the base; and securing the cap to the base to form a container completely enclosing the test strip except for the ports. Preferably, the securing includes grasping the test strip between the cap and the base. Preferably, the securing includes compressing the test strip. Preferably, the securing comprises snapping a locking member into a groove. Preferably, the securing comprises sonic welding.
In still another aspect, the invention provides a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the system comprising: a container having a sidewall and a bottom enclosing a test volume wherein the sidewall and bottom are essentially impervious to liquid, and at least a portion of the sidewalls or bottom is permeable to gas; a sample port above the container and communicating with the container; a sensor port communicating with the bottom; and a dry test strip in the test volume, the dry test strip containing a reagent capable of interacting with the bodily fluid to determine the characteristic. Preferably, the bottom comprises a material for which the surface tension of the bodily fluid in contact with the material is sufficiently high that the weight of the bodily fluid in the container will cause the bodily fluid to enter the material but not exit the bottom of the material. Preferably, the test strip includes one or more layers, and the bottom of the container is formed by the bottom layer of the test strip. Preferably, the bottom layer of the test strip comprises a nylon membrane in which the net charge can be controlled by changing the pH. Preferably, the test strip includes an asymmetric porous membrane, the asymmetric membrane having a first side and a second side, wherein the average pore size in the first side is larger than the average pore size in the second side, and wherein the first side faces the sample port. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood.
In yet another aspect, the invention provides a method of manufacturing a device for testing of bodily fluids, the method comprising: providing a test strip, the test strip impregnated with chemicals capable of a predetermined colorimetric response to a predetermined bodily fluid, the test strip having sufficient surface tension with respect to the bodily fluid so that the predetermined bodily fluid will pass into the test strip, but not out of it; forming a container having a container bottom and a sensing port formed in the container bottom; placing the test strip in the container so that it covers the sensing port. Preferably, the forming a container comprises forming a fluid impenetrable wall that completely surrounds a sample space, and the placing comprises placing the test strip in the sample space. Preferably, the method further comprises securing a cap on the container while compressing the test strip between the cap and the container.
In another aspect, the invention provides a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the system comprising: a container having a sidewall and a bottom enclosing a test volume and a sample port, the sidewall and bottom being essentially impervious to liquid; an asymmetric porous membrane within the test volume; and a dry test strip in the test volume, the dry test strip containing a reagent capable of interacting with the bodily fluid to determine the characteristic. Preferably, the asymmetric porous membrane comprises polysulfone. Preferably, the asymmetric membrane has a first side and a second side, wherein the average pore size in the first side is larger than the average pore size in the second side, and wherein the first side faces the sample port. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood.
In a further aspect, the invention provides a system for determining a characteristic of a bodily fluid, the system being portable and of a size that can be easily held in a human hand, the system comprising: a housing defining a test volume; a sample port in fluidic communication with the test volume; a test strip assembly comprising a first test layer, a second test layer, and a third test layer; the first test layer being closer to the sample port than the second test layer, and the third test layer being farther from the sample port than the second test layer; the first test layer comprising a woven material; the second test layer comprising non-woven fibers; the third test layer comprising an asymmetric membrane; and a reagent in the test volume, the reagent capable of interacting with the bodily fluid to determine the characteristic. Preferably, the asymmetric membrane has a first side and a second side, wherein the average pore size in the first side is larger than the average pore size in the second side, and wherein the first side faces the sample port. Preferably, the asymmetric membrane comprises polysulfone. Preferably, the second test layer comprises a hydroxylated polyester. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood.
The invention also provides a method for determining a characteristic of a bodily fluid; the method comprising: applying a bodily fluid to a portable testing system that can be easily held in a human hand and which includes a sample container containing a test strip; permitting the bodily fluid to flow vertically downward into the container; stopping the flow of the bodily fluid in the container; reacting a portion of the bodily fluid to create a colorimetric indicator of a parameter of the bodily fluid; and reading the colorimetric indicator without removing the bodily fluid or the test strip from the container. Preferably, the method further includes permitting air in the container that is trapped by the bodily fluid to flow out of the bottom of the container. Preferably, the bodily fluid is blood containing red blood cells, and the method further includes slowing the flow of red blood cells in the vertically downward direction. Preferably, the bodily fluid is blood and the characteristic comprises the concentration of high density lipoproteins or low density lipoproteins in the blood. Preferably, the method comprises complexing a lipoprotein in the bodily fluid so that it does not take part in the colorimetric reaction, wherein the complexing is done without precipitating the lipoprotein. Preferably, the complexing comprises exposing the lipoprotein to a reagent comprising dextran sulphate and a divalent metal.
The invention further provides a method of determining a characteristic of a selected one of a plurality of analytes in a bodily fluid, the method comprising: providing the bodily fluid containing the selected analyte and one or more non-selected analytes; reacting the selected one of the analytes with a reactant to provide a colorimetric indication of the characteristic; and, prior to the reacting, preventing the non-selected analytes from participating in the reaction, without precipitating the non-selected analytes.
One benefit achieved by the dry strip architecture of the present invention is that the performance of the strip is essentially volume independent. Since the test strip architecture eliminates the risk of cross-contamination, once the bottom layer of the test strip is saturated, the sample flow stops. Thus, the present invention can accommodate a blood sample as large or larger than the test well. On the other side of the spectrum, the present invention accommodates a sample size essentially as small as the volume of the bottom reaction layer. The present strip architecture limits the fluid expansion area so that the vertical column can be limited to nearly the diameter of the viewing window at the base of the strip. In the preferred embodiment of the invention, the test strip architecture can accept a sample volume as small as 4 ml to as large as 40 ml, while still delivering accurate test results.
Another benefit of the present invention is that the test strip architecture provides greater control over the vertical flow of the sample. As explained above, once the bottom layer of the strip is saturated, sample flow stops which means that the flow of red blood cells also stops. When the flow of RBCs stops, there is no further need for capturing the RBCs. This aspect of the present invention allows the use of a less efficient RBC capturing layer, since the sample flow physics will stop the flow of RBCs at the optimum point.
It is one object of the invention to provide a holder for a diagnostic test strip that can maintain the integrity of the test strip without risking damage to it. Another object is to provide a test strip assembly architecture that can improve the accuracy of the diagnostic output. These and other objects and benefits of the invention will become apparent from the following written description and accompanying figures.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. It should also be understood that, in accordance with the patent law, the drawings are not intended to be precise engineering drawings of the invention, but rather are only intended to illustrate the invention. For example, the scale of the drawings and relative size of the various parts are generally altered so as to better illustrate the invention within the constraints of a written document such as this.
An exploded perspective view of the test assembly 20 is shown in
The holder base 60 is shown in
Cap 40 is shown in
Test strip 50 is shown in
The test strip assembly 20 is assembled as shown in
Turning to
Cap 170 comprises a preferably ring-shaped cap flange 173 with a brim 149, which is preferably rounded and integrally formed with flange 173. A groove 171 is formed between cap flange 173 and brim 149 that is configured for snap-fit or press-fit engagement with an annular lip 169 and ramp 167 of retainer 190 of the holder base 60. Flange 173 includes a projecting distal end 172 that bears against and compresses the test strip 150 within the well 162. To avoid damage to the test strip, the flange distal end 172 includes an upwardly and radially outwardly sloped edge 174 that merges into an interior radiused edge 175 at the sample opening 176 of the cap. As can be seen in
A further alternative embodiment of a test assembly 200 is shown in a cross-sectional view in
As known in the art, the carrier body 30, 130, etc., holder base 60, 160, 228, 360, and cap or cover 40, 170, 240, 340 are preferably made of plastic or other suitable material. Preferably, the plastic parts are injection molded, and cap 40 is sonic welded to holder base 60 at locator tabs 68. Thus, the placement tabs enable the cap to be welded without contact with the main body of cap 60. Preferably, the plastic parts, particularly the cap 40, are color-coded to correspond to the particular test, such as HDL, LDL, total cholesterol, etc., for which the test strip assembly, such as 50, is designed.
Preferably, for the exemplary HDL test, there are four layers 52, 54, 56, and 58, best shown in
The next layer 54 contains the reagents that interact with the non-desired analytes that would compromise the colorimetric test to be performed in layer 58, so that these analytes do not participate in the colorimetric reaction. For example, if the colorimetric test in layer 58 is to be a test for HDL, analytes, such as LDL (low density lipoproteins), VLDL (very low density lipoproteins), ILDL (intermediate density lipoproteins), and chylomicrons (big, tryglyceride-rich lipoproteins), that may make the test less accurate or reliable are interacted with in some way that prevents them form participating in the colorimetric reaction in layer 58. Preferably, the reaction is one in which these analytes are bound in clusters within a compound that prevents them from reacting. The specific reagents are described in copending U.S. patent application Ser. No. 10/962,272 filed Oct. 11, 2004 and U.S. patent application Ser. No. ______ (Patton Boggs Docket No. 23134.0118PTUS) filed on even date herewith, which patent applications are hereby incorporated by reference as though fully disclosed herein.
Layer 54 is also preferably a depth filter, which functions to reconstitute the reagent; that is, get the dried reagent into solution. A key feature of this layer 54 is that it includes many small fibers, and thus it has a large surface area. Preferably, the fibers are random; that is, they are not organized as in a weave. This type of filter is often referred to as a conjugate relief pad, wicking pad, sample pad, or prefilter. The surface area is preferably such that the wicking rate is below 8 seconds per two centimeters. Preferably, the surface area should be such that after wetting with the reagent and drying, the layer holds a weight of dry reagent equal to the membrane weight itself. Preferably, the weight of the dry agent should not be lower than 75% of the weight of the membrane and not above 125% of the weight of the membrane. Since the reagent is on the surface of the fibers, the large surface area helps to reconstitute the reagent faster, since there is a larger area of reagent exposed to the solvent. Preferably, the average pore size of this layer is controlled to optimally control flow through the layer so that the bodily fluid remains long enough to reconstitute the reagent, but not so long as to delay or otherwise hinder the test in layer 58. The controlled pore size in combination with the large surface area helps to limit or retard the movement of the solute in the vertical direction so that it remains in the material longer, and thus has more time to dissolve the reagent. Preferably, layer 54 is made of a non-woven, fibrous material such as a hydroxylated polyester, preferably a polyhydroxylated polyester. Suitable such materials are membranes made by Pall Life Sciences, such as Accuwik Ultra™. Preferably, the membrane is inserted with the bumps side down.
The purpose of the next layer 56 is preferably to remove red blood cells from the analyte liquid and to further add to the reagent/solvent contact time to continue the process of getting the reagent into solution. It is preferably made of an asymmetrically porous material; that is, the pore size varies through the material. Preferably, the side with the large pores is up. In the preferred embodiment, it has a pore size of between 250 microns and 350 microns, and more preferably 300 microns, on the sample-receiving side, and a pore size of between 0.5 microns and 10 microns, and preferably 3 microns, on the detection side. The preferred material is an asymmetric polysulfone such as is BTS-SP-300 or BTS-SP-200 available from Pall Life Sciences, or other suitable materials may be used. Other suitable materials are lechtin-coated graphite fibers, ruthenium oxide fiber, and other materials known in the art. The asymmetric nature of the layer 56 is effective in removing red blood cells while continuing the movement of the solvent and reactant downwards. In the preferred embodiment, it removes the red blood cells by slowing them as they percolate through the tortuous path of the pores. As the pores get smaller, the red blood cells may also become entangled in the fibers, but this happens gradually and relatively randomly throughout the layer, rather than collecting all at one level within the test strip, as they would in a conventional filter with a single pore size; such collecting all at one level tends to block fluid flow. The relatively random entrapment of the red blood cells leaves open capillary paths through the material. Such capillaries assist in drawing the fluid downward through the test strip 50, particularly since the capillaries become smaller in that direction. As will be seen more clearly below, however, it is only necessary to slow the red blood cells to separate them. That is, because the bottom of container 80 is essentially closed, flow stops when the layer 58 becomes saturated. If flow stops and the red blood cells are still in the upper layers, they will remain there.
Bottom layer 58 is the detection layer and contains the detection reagent. It is preferably made of a hydrophobic material which has sufficient surface tension with the analyte bodily fluid so that the fluid will not flow past it. In the preferred embodiment, the test strip assembly layers 52-58 are circular and are all of the same diameter, though other shapes and sizes may be used. The preferred detection layer 58 is the Biodyne™ A membrane available from Pall Corporation with the total cholesterol formulation described in United States Patent Application Publication US 2004/0126830 on application Ser. No. 10/663,555 filed Sep. 16, 2003, which is hereby incorporated by reference to the same extent as though fully disclosed herein. This membrane is a nylon membrane in which the net charge can be controlled by changing the pH. As disclosed in the foregoing reference, the reagents are Trinder reagents which include enzymes, such as cholesterol oxidase, perosidase, and cholesterol esterase, that react with cholesterol to effect a color change which can be detected optically.
Layers 472 and 474 are preferably optional layers used in controlling timing of the reconstitution of the reagent in layer 456. For example, membrane 472 may be a Supor™ 1200 untreated membrane. This example has relatively large 1200 micron pores. It is used to slow down the percolation of the analyte liquid through the assembly to give the reagent introduced in layer 456 more time to dissolve. The smaller the pores in layer 472, the more it slows down the analyte. Layer 474 is an optional layer, preferably having asymmetrical pores 477, that may be identical to layer 456, and is included if it is desired to put more reagent in solution, or to put less reagent in layer 456 so that it dissolves more easily. Layer 458 is a reagent layer which is illustrated by showing a fiber 457 with a reagent 459 on its surface. This reagent is the colorimetric reagent that reacts with the analyte to produce the color, the reflectance of which provides the test result. Layer 476 is a layer in which the individual fibers 466 are preferably hydrophobic, which means they tend to repel water; that is, preferably, water has a high surface tension on the material. Water will tend not to penetrate this material. However gas, such as air, will pass easily through this material. Preferably, the material of layer 476 is an open pore material, and/or also holds a relatively large amount of fluid, as compared to membranes such as 456. However, it also may be an asymmetric membrane with the larger pores on the upper side 467. Such a material tends not to hold large amounts of fluid, but makes the fluid available to the reaction layer 458, as will be discussed in more detail below. Layer 476 is also preferably very thin and/or transparent, particularly when it is saturated with liquid, so that the color in layer 458 can be sensed through it. In the embodiments of
The test strip operates generally as follows. A drop of bodily fluid, such as blood, is placed within the sample application port 45 of cap 40. It is evenly dispersed across the opening by test strip layer 52 and percolates vertically downward. The pall membrane 54 separates the unwanted material, such as the red blood cells, from the rest of the fluid, such as the serum. The red blood cell filtration/reagent membrane 56 includes reagents that react with undesired analytes that would compromise the test in membrane 58. For example, if the test in membrane 58 is for HDL, the LDL, ILDL, VLDL, and chylomicron portions of the serum are complexed in membrane 56. The membrane tends to slow or retain the complexed lipoproteins, but allows the HDL to pass to reagent layer 58. The HDL reacts in reagent layer 58 to turn the layer a predetermined color, which is detected by spectrophotometer device 10. However, it is not necessary that membrane 56 retains or even slows the complexed undesired lipoproteins. The complexing itself prevents the undesired analytes from participating in the reaction in test membrane 58 and thus takes these analytes out of the reaction that determines the color. Detailed examples of the chemicals used in the test strip layers and the chemical reactions that take place in the test strip layers are described in copending U.S. patent application Ser. No. 10/962,272 filed Oct. 11, 2004 and U.S. patent application Ser. No. ______ (Patton Boggs Docket No. 023134.0118PTUS) filed on even date herewith. The foregoing patent applications describe the preferred chemistry, which is non-precipitating. However, conventional precipitating chemistry as is known in the art also works well with the system according to the invention, and the invention also provides significant improvements in accuracy when used with the prior art chemistries.
A test strip element 50 was made by assembling a sheet of SEFAR™ type 76 SK 022 and the three sheets discussed above impregnated with chemicals as disclosed in the above-referenced patent applications, and cutting out circular blanks, which were inserted in a test assembly 20 as shown in
A feature of the invention is that each layer of the test strip assembly, such as 50 and 450, is engineered to perform specific functions, and at the same time the various layers cooperate so that the test strip assembly as a whole operates to provide more accurate and reliable results. The layers together operate to create a vertical flow of sample liquid essentially across the entire test strip assembly. The red blood cells tend to move slower than the rest of the sample, or get removed from the sample in the layers 54, 56, 454, 456; and therefore, during the time in which the colorimetric reagent is reacting, they will be contained in the layers above the reaction layer and will not be in the reaction layer 58, 458. However, the other analytes may or may not be in the reaction layer 58, 458. Since they are rendered non-reactive by the reagents in layer 54, 454, whether or not they are present is not of great importance. The non-desired analytes are preferably not precipitated, so the pores or channels in the layers 56, 58, 456, 458, and 460 remain open. This allows the sample liquid in the layers 56, 456, 460 adjacent to the reaction layer 58, 458 to participate in the colorimetric reaction. That is, in the embodiment of
An important feature of the invention is that the structures of the invention create a sample container, 80, 189, 280, 380, and 480, the sidewalls and bottom of which essentially do not pass liquid, and the top of which is open. This creates several advantages that result in a more accurate and reliable measurement. First, it results in a well-defined test volume of sample fluid. When the bodily fluid is added to the container, it flows to the bottom, and then stops. Only the bodily fluid in the reagent layer, and the adjacent layers in test strips in which the open pore feature discussed above is used, takes part in the reaction. Moreover, at the time of the reaction, this volume is essentially quiescent. Thus, a defined volume of fluid participates in the reaction. This duplicates much more closely the laboratory type test in which a beaker with a defined volume is used in tests, as compared to prior art test strips in which flow, particularly transverse flow, continued to occur during the test, which flow could depend on many variables and was difficult to quantify. Moreover, the fact that flow stops prevents red blood cells from getting through the layers above the test layers. That is, once flow stops, there is no flow or pressure to move the red blood cells. Thus, the layers above the test layer do not have to be completely impenetrable to red blood cells. All they have to do is slow the red blood cells for a while until the test volume is filled. This again plays back into the feature that the red blood cells do not completely block the pores, but permit ease of fluid flow once the reagent is reconstituted. In general, the object of the layers 54 and 56 is to contain the red blood cells in this region and not permit them to get into the reaction layer 58. However, the containment of the red blood cells in layers 54 and 56 does not have to be absolute. Preferably, the containment of the red blood cells is at least 50%, more preferably it is at least 80%, and most preferably at least 95%.
In the inventive test, if more bodily fluid than is required for the test is placed in the sample port, such as 45, the fluid in excess of what is required for the test simply fills up the upper portion of the container, such as 80, and does not affect the test. If the excess is too much even for the container, the excess simply overflows the brim 46 and does not affect the test. Thus, the bodily fluid analysis system according to the invention is much less sensitive to the amount of bodily fluid supplied than prior art systems.
The above feature of the invention, i.e., that the test strip holder 24 provides a sample container 80, 189, 280, 380, and 480, the sidewalls and bottom of which essentially do not pass liquid and therefore the test is performed on a well-defined volume of fluid, also increases the accuracy of the test because it provides a definitive end point to the test. This can be understood by referring to
Another feature of the invention is that the bottommost layer, such as 58 and 460, which forms the bottom of container 80, 180, 280, 380, 480, preferably does not pass liquid, but passes gases, such as air. This feature prevents air from being trapped at the bottom of the container, such as 80, when the bodily fluid is added. Any air that does not bubble out of the container is forced downward and out of the bottom of the container by the flow of bodily fluid. This removes an unquantifiable variable from the test and makes the test more accurate and reliable.
A feature of the invention is that the portion of the cap that contacts the test trip, e.g., the arm 44, and the portion of the holder base that contacts the test strip, e.g., test strip support 69, engages the entire perimeter of the test strip about the sensor port. A further feature is that the engaging arm 44 and test strip support 69 are essentially directly opposed on either side of the test strip. These features create a uniform pressure on the test strip about its entire perimeter and seal the perimeter. A further feature is that sharp surfaces that engage the test strip are virtually eliminated. The combination of the uniformity of the pressure exerted by the arm, such as 44, and test strip support, such as 69, and the elimination of sharp surfaces eliminate tearing or other damage to the test strip. In the prior art, this damage to the test strip was a significant contribution to test inaccuracies or test failures.
A related feature of the invention is that the test strip holder provides a controlled region for vertical flow of the bodily fluid sample. These features, alone and in combination, eliminate or sharply limit leaching or lateral flow of the sample as bodily fluid flows vertically through the layers. This degree of control translates to the ability to obtain accurate test readings from a reduced blood sample. Accurate results can be obtained with a sample size of as low as 4 ml and as great as 40 ml with the present invention.
A further feature of the invention is that the test strip assembly, such as 50, preferably does not include any glue, adhesive, or other substance to hold it in place. Such substances can get into the test sample and compromise the test to make it less accurate and reliable.
Another feature of the invention is that the reagents used, particularly those in layer 54, are non-hemolytic. That is, they will not rupture the red blood cells. This prevents the matter from inside the red blood cells from compromising the test. Preferably, the reagents are hypertonic; that is, the reagent in solution has a higher osmotic pressure than the osmotic pressure within the red blood cells. Thus, if there is any flow of water, it will be from within the cell to outside the cell. The reverse could cause the cells to gain water until they rupture. However, the reagents are selected so that the degree of hypertonicity is low. Otherwise, the liquid from with the blood cells could dilute the bodily fluid to be analyzed.
Another feature of the invention is that the interrelationship between reagent formulation and the liquid flow in the materials of the test strip layers is considered. That is, the effect of the reagent on the surface tension of the fluid and the effect of the resulting surface tension on the rate of flow through the layers are considered. For example, water will generally not flow easily in the layers according to the invention. The membranes, in particular, tend to hold water like a sponge. However, water with the reagents dissolved flows easily in these membranes. This feature helps keep the liquid in the depth filter until the reagents are dissolved.
The test strips, such as 50, 150, 250, 350, and 450, according to the invention are highly sophisticated compared to the prior art test assemblies. The prior art test strips tended to simply include materials, such as fiberglass, that could hold a large amount of bodily fluid and reagent. They succeeded largely because they used large amounts of both bodily fluid and reagent. In contrast, the test strip assemblies according to the invention utilize many different materials that are carefully chosen and engineered, and they succeed because they better isolate the desired reaction. Because of this, the test strip assemblies of the invention can operate effectively with a much smaller amount of reagent, and thus are more economical than the prior art test strips.
The design methodology of the invention is a self-consistent and self-reinforcing process. The materials and chemical processes of the invention are carefully engineered so that more accurate and more reliable results can be achieved with a smaller amount of reagent and a correspondingly smaller test strip assembly. Because the results that can be achieved are more accurate and can be achieved with a smaller amount of reagent, more flexibility is permitted in the selection of materials in the layers and the reagents. For example, membranes that retain and hold relatively small amounts of liquid can be selected over fabrics that hold large amounts of fluid, while fabrics that hold large amounts of fluid can also be used advantageously where appropriate. The ability to use a wider variety of materials enables the engineer to design a test that is closely akin to a laboratory analysis. That is, laboratory analyses can be very accurate because the order and timing of the reactions can be carefully controlled. One can add an accurately measured amount of a first reactant to an accurately measured amount of solvent, allow a first reaction to occur, then add an accurately measured amount of second reactant and perform a second reaction, and so on. The ability to use a wide variety of different materials allows one to control the order and timing of the reactions in a similar manner. The first reaction is placed closest to the top in the vertical structure of the test strip assembly. The timing of the second reaction can be controlled by choosing the materials of the first reactant layer and the adjoining layers to control the flow time through the layers, and so on.
While the invention has been disclosed in terms of an HDL or LDL direct assay, it will be evident to those skilled in the art that many aspects of the invention will be useful in other assays. Now that a dry test strip assay has been disclosed that mimics many of the features of a laboratory assay, such as use of a well-defined test volume, reaction order and timing controls using a variety of materials, and the ability to remove red blood cells from the reaction while still providing the above two features, these features may also be used to test for total cholesterol, triglycerides, ketones, and many other analytes. Further, now that the advantages of a non-precipitating dry test strip, asymmetric membranes, removal of red blood cells from the detection area without filtering that can clog the system are known, these features can also be advantageously used for testing of other analytes. Further, although the description has disclosed specific exemplary material layers that perform the features of the invention, now that the functions of the layers and the interrelationships of the layers has been described, many other materials can be substituted which will perform the same functions. In addition, while the invention has been disclosed in terms of specific exemplary reactants, many other reactants that perform the same functions and have some or all of the same advantages can be substituted. Again, while the invention has been disclosed in terms of a particular bodily fluid, i.e., blood and blood plasma, many features of the invention will be useful in testing other bodily fluids, such as urine. Thus, the invention should not be limited to these specific structures, layer materials, reactants, and bodily fluids.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications, and further applications that come within the spirit of the invention are desired to be protected. For instance, while the illustrative embodiments only show a single sample application port and a single corresponding sensor port, multiple sample ports and multiple sensor ports are contemplated.
There has been described a novel invitro, dry test system that is useful to assay for HDL and other analytes. It should be understood that the particular embodiments shown in the drawings and described within this specification are for purposes of example and should not be construed to limit the invention, which will be described in the claims below. Further, it is evident that those skilled in the art may now make numerous uses and modifications of the specific embodiments described, without departing from the inventive concepts. For example, while the ports and test strips have been shown as circular, other shapes may also be used. Additional layers may be added to the test strip assembly. As a further example, any of the caps, such as 60, may be attached to a flap, such as described in U.S. Pat. No. 5,597,532, which would permit the cap, such as 60, and body, such as 30, to be made in a single piece in which the cap and body are connected. This has some advantages in parts management. It is also evident that the methods recited may in many instances be performed in a different order; or equivalent structures and processes may be substituted for the various structures and processes described. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in and/or possessed by the bodily fluid analysis system herein described.
This application is a continuation-in-part of U.S. patent application Ser. No. 10/962,272 filed Oct. 11, 2004, which claims the benefit of U.S. Provisional Application No. 60/541,681 filed Feb. 3, 2004. This application also claims the benefit of U.S. Provisional Application No. 60/602,210 filed Aug. 17, 2004. All of the above patent applications, both provisional and non-provisional, are hereby incorporated by reference to the same extent as though fully contained herein.
| Number | Date | Country | |
|---|---|---|---|
| 60541681 | Feb 2004 | US | |
| 60602210 | Aug 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10962272 | Oct 2004 | US |
| Child | 11207121 | Aug 2005 | US |
