CN114502951A

CN114502951A - Contamination determination for biosensors of analyte measurement systems

Info

Publication number: CN114502951A
Application number: CN201980100729.7A
Authority: CN
Inventors: D·麦科尔; A·麦克雷; G·麦菲; S·麦金托什; D·莫里斯; J·沃特
Original assignee: Life Scan Intellectual Property Holding Co ltd
Current assignee: Life Scan Intellectual Property Holding Co ltd
Priority date: 2019-07-24
Filing date: 2019-07-24
Publication date: 2022-05-13
Also published as: CA3148386A1; EP4004535A1; JP7371219B2; WO2021015755A1; CA3148386C; WO2021015755A9; JP2022542568A

Abstract

A method for determining contamination of a biosensor, wherein the biosensor is loaded into a test meter and then a sample is applied. First and second predetermined test voltages are applied between spaced electrodes of the biosensor in respective first and second predetermined time intervals. First and second current values are measured during respective first and second predetermined time intervals. A reference value is determined based on the measured first and second current values. Based on one or more of the reference values, contamination is determined. Based on the determination, reporting of the analyte concentration of the sample may be suppressed.

Description

Contamination determination for biosensors of analyte measurement systems

Technical Field

The present application relates generally to analyte measurement systems and, more particularly, to methods for determining contamination, such as moisture contamination of a biosensor for an analyte measurement system.

Background

Analyte detection in physiological fluids (e.g., blood or blood-derived products) is of increasing importance to today's society. Analyte detection assays find use in a variety of applications, including clinical laboratory testing, home testing, and the like, where the results of such testing play an important role in the periodic diagnosis and management of various disease conditions. Analytes of interest include glucose and cholesterol, among others, for diabetes management. To address the growing importance of analyte detection, a variety of clinical and in-home testing protocols and devices have been developed.

One method for analyte detection of a liquid sample is an electrochemical method. In this method, an aqueous liquid sample (such as a blood sample) is deposited onto a biosensor and filled into a sample-receiving chamber of an electrochemical cell comprising two electrodes, e.g., a counter electrode and a working electrode. The analyte is allowed to react with the redox reagent to form an oxidizable (or reducible) substance in an amount corresponding to the analyte concentration. The amount of oxidizable (or reducible) substance present is then estimated electrochemically and related to the amount of analyte present in the deposited sample.

For example, one of the blood glucose measurement systems manufactured by LifeScan corporation and sold as one-touch Verio ("Verio") has shown very good overall performance and accuracy.

However, any analyte measurement system may be susceptible to various inefficiencies and/or error patterns. For example, biosensors used in analyte measurement systems, such as disposable test strips, may become contaminated or damaged when stored by a patient for self-administered blood tests, such as blood glucose tests. Unfortunately, contaminated or damaged test strips may result in erroneous or higher than expected analyte concentration measurements. These erroneous measurements can mislead the subject to administer the wrong dose of the drug, leading to potentially catastrophic consequences. Therefore, there is an urgent need to determine whether a critical amount of contamination or damage to the biosensor has actually occurred before reporting the analyte measurement results.

Drawings

For the purpose of illustrating the features of the disclosure, reference will now be made in detail to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the appended drawings illustrate only certain embodiments and are therefore not to be considered limiting of its scope, for the scope of the disclosed subject matter encompasses other embodiments as well. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments. In the drawings, like numerals are used to indicate like parts throughout the various views.

FIG. 1 illustrates a perspective view of an analyte measurement system including a test meter and a biosensor (test strip) according to aspects set forth herein;

FIG. 2 is a top view of a circuit board disposed in the test meter of FIG. 1, depicting various components according to aspects set forth herein;

FIG. 3A is a perspective view of an assembled test strip suitable for use in the analyte measurement system of FIGS. 1 and 2;

FIG. 3B is an exploded perspective view of the test strip of FIG. 3A;

FIG. 3C is an enlarged perspective view of a proximal portion of the test strip of FIGS. 3A and 3B;

FIG. 3D is a bottom plan view of the test strip of FIGS. 3A-3C;

FIG. 3E is a side elevational view of the test strip of FIGS. 3A-3D;

FIG. 3F is a top plan view of the test strip of FIGS. 3A-3E;

FIG. 3G is a partial side elevational view of a proximal portion of the test strip of FIGS. 3A-3F;

FIG. 4 is a simplified schematic diagram showing a partial electrical engagement of a test meter with a test strip (such as the test strip depicted in FIGS. 3A-3F);

FIG. 5A illustrates an example of a test waveform applied by the test meter of FIG. 4 to the working and counter electrodes of a test strip over a prescribed time interval for determining an analyte in a sample applied to the test strip;

FIG. 5B depicts the change in current over time measured based on the waveform of FIG. 5A for a nominal test strip;

FIG. 5C is a flow chart illustrating a method for determining the concentration of an analyte in a test strip;

FIG. 6A depicts a graphical comparison illustrating the measured current value between a nominal test strip and a contaminated test strip over time based on a portion of the waveform of FIG. 5A; and

fig. 6B is a flow chart representing a method for determining the presence of contamination in a test strip according to aspects set forth herein.

Detailed Description

The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. The description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

As used herein, the term "about" or "approximately" for any numerical value or range indicates a suitable dimensional tolerance that allows the portion or collection of components to be used for the intended purpose described herein. Furthermore, as used herein, the terms "patient," "host," "user," and "subject" refer to any human or animal subject, and are not intended to limit the system or method to human use, although the use of subject technology in human patients represents a preferred embodiment.

The present disclosure relates in part to techniques for utilizing a biosensor, such as a disposable test strip, to determine whether the biosensor has been contaminated or compromised prior to conducting a test for determining an analyte concentration of an applied sample. In addition to moisture contamination, these techniques may also be applied to test strips that have been exposed to extreme temperatures (e.g., well above typical room temperatures), excessive light, higher humidity levels, and the like. Such contamination or exposure, which may result from improper storage, can result in a certain amount of mediator being converted at the test strip electrodes, for example from potassium ferricyanide to potassium ferrocyanide. In one example, a moisture-contaminated blood glucose test strip may have a falsely higher than expected result that is approximately 80 mg/dL (or higher) higher than the actual blood glucose value. In such a case, such a higher than expected measurement value may result in administering an incorrect high dose of insulin to the patient, resulting in a serious impact on the patient's health.

Conversely, if a small amount of moisture contaminates the test strip so that the test strip can still give results within an acceptable range of accuracy, the test results should be displayed to the patient. Thus, a simple method of merely determining that some unknown levels of moisture have contaminated the test strip would not solve the problem of merely eliminating the above-expected results, and would reduce the therapeutic outcome of the patient by increasing the cost of the blood glucose test. In addition, the technology that requires new test meters or additional physical test strips would be incompatible with previously deployed units, which also increases cost. Furthermore, any contamination-determining test of the test strip will only be effective if the test itself is not damaged or prevented from being used to perform the analyte measurement.

While the Verio system discussed above has very good overall performance, testing has shown that biosensors are not completely immune to contamination, such as may result from improper storage of the test strips. Such contamination may include moisture contamination or contamination by other external sources or stimuli (temperature, light, humidity). In an attempt to find a way to reduce the effects of contamination, a technique is provided herein to alert the user of a test strip that the test strip will produce erroneous results due to contamination based on storage and environmental conditions. Accordingly, various aspects of a method of determining whether a biosensor is contaminated are presented herein. In one example of the present technology, analyte measurements may be taken concurrently with the contamination determination, such that if the biosensor is not deemed contaminated or damaged, the test results may be issued (displayed) to the patient. Also, if the test strip is deemed contaminated, the test results may be suppressed to avoid giving the patient a higher than expected analyte reading, which may result in an improper drug dose.

In general, and in accordance with at least one embodiment, a method for determining biosensor contamination is provided. The biosensor is loaded into the test meter and a sample is applied to the biosensor. A first predetermined voltage is applied between the spaced electrodes of the electrochemical cell for a first predetermined time interval and a second predetermined voltage is applied between the spaced electrodes during a second predetermined time interval after the first predetermined time interval. A first current value is measured during a first predetermined time interval. The first reference value is determined based on a sum of the first current values during a first predetermined time interval. A second current value is measured during a second predetermined time interval. A second reference value is determined based on the peak current value measured during a second predetermined time interval. The third reference value is determined based on a rate of change of the current value measured after the peak current value during the second time interval. Whether the biosensor is contaminated may be determined based on one or more of the first to third reference values. When it is determined that the biosensor is contaminated, reporting of the analyte concentration is suppressed. In another embodiment, a test meter is proposed which performs the above-mentioned method steps.

The above-described embodiments are intended to be examples only. Other embodiments are also within the scope of the disclosed subject matter, as will be readily apparent from the following discussion.

Specific working examples will now be described with reference to fig. 1-6.

Fig. 1 illustrates a diabetes management system that includes a portable test meter 10 and a biosensor provided in the form of a disposable test strip 62 configured for detecting blood glucose. For purposes of the following discussion, portable test meters are synonymously referred to throughout as analyte measurement and management units, glucose meters, meters and/or meter units. Although not shown in this view and at least one embodiment, the portable test meter may be combined with an insulin delivery device, an additional analyte test device and a drug delivery device. The portable test meter may be connected to a remote computer or remote server via a cable or suitable wireless technology such as, for example, GSM, CDMA, bluetooth, WiFi, etc. Such Analyte Measurement systems are described in U.S. patent nos. 8,709,232B2 entitled "Analyte Measurement Technique and System" entitled "Analyte Measurement techniques and systems" entitled "System and Method for Measuring an Analyte in a Sample" and international patent publication No. WO 2012/012341 a1 entitled "System and Method for Measuring an Analyte in a Sample", granted on day 4 and 29 2014, each of which is incorporated herein by reference in its entirety.

Still referring to FIG. 1, the portable test meter 10 is defined by a housing 11, the housing 11 having a plurality of user interface buttons (16, 18, and 20) disposed on a facing surface. In addition to the test strip port opening 22, which is configured to receive a biosensor (test strip 62), a display 14 is provided. The user interface buttons (16, 18, and 20) may be configured to allow data entry, menu navigation, and command execution. It will be apparent that the configuration and function of the user interface buttons of the portable test meter 10 are intended to be examples, and that modifications and variations are possible. According to this particular embodiment, the user interface buttons 18 may be in the form of two-way toggle switches. The data may include values representative of analyte concentrations and/or information related to an individual's daily lifestyle. Information related to daily lifestyle can include food intake, drug use, occurrence of health checks, and general health and exercise levels of an individual.

As shown in fig. 2, and in simplified schematic form, the electronic components of the portable test meter 10 may be disposed on a circuit board 34, the circuit board 34 being contained within the interior of the housing 11 of fig. 1. According to this embodiment, the electronic components include test strip port connector 23, operational amplifier circuit 35, microcontroller 38, display connector 14a, non-volatile memory 40, clock 42, and first wireless module 46. On the opposite bottom surface of the circuit board 34, the electronic components may include a battery connector (not shown) and a data port 13. It should be understood that the relative positions of the various electronic components may vary, and that the configurations described herein are exemplary.

Microcontroller 38 can be electrically connected to test strip port connector 23 (fig. 1) aligned with test strip port opening 22, operational amplifier circuitry 35, first wireless module 46, display 14, non-volatile memory 40, clock 42, at least one battery (not shown), data port 13, and user interface buttons (16, 18, and 20).

The operational amplifier circuit 35 may include two or more operational amplifiers configured to provide a portion of the potentiostat function and the current measurement function. Potentiostat function may refer to the application of a test voltage between at least two electrodes of a test strip. The current function may refer to a measurement of a test current resulting from an applied test voltage. The current measurement may be performed with a current-to-voltage converter. Microcontroller 38 may be in the form of a mixed signal Microprocessor (MSP) 430, such as, for example, a Texas Instruments (TI) MSP. The MSP 430 can be configured to also perform a potentiostat function and a portion of the current measurement function. In addition, 430 may also include volatile and non-volatile memory. In another embodiment, many electronic components may be integrated with the microcontroller in the form of an Application Specific Integrated Circuit (ASIC).

The test strip port connector 23 may be configured to form an electrical connection with the test strip 62. Display connector 14a may be configured to attach to display 14. For purposes of this description, the display 14 may be in the form of a liquid crystal display for reporting measured glucose levels and facilitating the entry of lifestyle-related information. Display 14 may optionally include a backlight. The data port 13 may accept a suitable connector attached to the connecting leads, allowing the test meter 10 to be linked to an external device, such as a personal computer (not shown). For the purposes of this description, data port 13 may be any port that allows data transfer, such as, for example, a serial, USB, or parallel port. The data port 13 is accessible through the housing 11 of the portable test meter 10. The clock 42 may be configured to maintain a current time associated with the geographic area in which the user is located and also to measure time. The test meter may be configured to be electrically connected to a power source, such as, for example, at least one internal battery (not shown).

Fig. 3A-3G illustrate various views of a test strip 62 suitable for use with the methods and systems described herein. In an exemplary embodiment, the test strip 62 is defined by an elongated body extending from a distal end 80 to an opposite proximal end 82 and having

lateral edges

56, 58, as shown in fig. 3A. As shown in fig. 3B, the test strip 62 also includes a first electrode layer 66, a second electrode layer 64, and a spacer 60 sandwiched between the two

electrode layers

64 and 66 at a distal end 80 of the test strip 62. The first electrode layer 66 may include a first electrode 66, a first connection rail 76, and a first contact pad 67, wherein the first connection rail 76 electrically connects the first electrode 66 to the first contact pad 67, as shown in fig. 3B and 3C. Note that as indicated in fig. 3A and 3B, the first electrode 66 is the portion of the first electrode layer 66 immediately below the reagent layer 72. Similarly, the second electrode layer 64 may include a second electrode 64, a second connection track 78, and a second contact pad 63, wherein the second connection track 78 electrically connects the second electrode 64 with the second contact pad 63, as shown in fig. 3A-3C. Note that the second electrode 64 is part of a second electrode layer 64 disposed over the reagent layer 72, as best shown in fig. 3B and 3C.

As shown, a sample-receiving chamber 61 (e.g., an electrochemical cell) is defined by a first electrode 66, a second electrode 64, and a spacer 60 near a distal end 80 of the test strip 62, as shown in fig. 3B-3E. As shown in fig. 3G, the first electrode 66 and the second electrode 64 may define the bottom and the top of the sample-receiving chamber 61, respectively. As shown in fig. 3G. The cutout region 68 of the spacer 60 may define a sidewall of the sample-receiving chamber 61. In one aspect, the sample-receiving chamber 61 may include a port 70 that provides a sample inlet and/or vent, as shown in fig. 3A-3C. For example, one of the ports 70 may allow the entry of a fluid sample and the other port 70 may allow the exit of air.

In an exemplary embodiment, the sample-receiving chamber 61 may have a small volume. For example, the volume of the sample-receiving chamber 61 may range from about 0.1 microliters to about 5 microliters, about 0.2 microliters to about 3 microliters, or preferably about 0.3 microliters to about 1 microliter. To provide smallnessThe incision 68 may have a sample volume ranging from about 0.01 cm²To about 0.2 cm²About 0.02 cm²To about 0.15 cm²Or preferably about 0.03 cm²To about 0.08 cm²The area of (a). Additionally, the first electrode 66 and the second electrode 64 may be spaced apart in a range of between about 1 micron and about 500 microns, preferably between about 10 microns and about 400 microns, and more preferably between about 40 microns and about 200 microns. The relatively close spacing of the electrodes may also allow redox cycling to occur, wherein oxidized mediator generated at the first electrode 66 may diffuse to the second electrode 64 to be reduced and then diffuse back to the first electrode 66 to be oxidized again. Those skilled in the art will appreciate that the volume, area, and/or spacing of various such electrodes are within the spirit and scope of the present disclosure.

In one embodiment, the first electrode 66 and the second electrode 64 may each include an electrode layer. The electrode layer may include a conductive material formed from a material such as gold, palladium, carbon, silver, platinum, tin oxide, iridium, indium, or a combination thereof (e.g., indium-doped tin oxide). In addition, the electrode layer may be formed by disposing a conductive material onto an insulating sheet (not shown) through sputtering, electroless plating, or screen printing process. In one exemplary embodiment, the first electrode 66 and the second electrode 64 may each include an electrode layer made of sputtered palladium and sputtered gold, respectively. Suitable materials that may be used as the spacer 60 include various insulating materials such as, for example, plastics (e.g., PET, PETG, polyimide, polycarbonate, polystyrene), silicon, ceramics, glass, adhesives, and combinations thereof.

In one embodiment, the spacer 60 may be in the form of a double-sided adhesive coated on opposite sides of the polyester sheet, wherein the adhesive may be pressure sensitive or heat activated. Applicants note that various other materials for the first electrode layer 66, the second electrode layer 64, and/or the spacer 60 are within the spirit and scope of the present disclosure.

Depending on the magnitude and/or polarity of the at least one applied test voltage, either the first electrode 66 or the second electrode 64 may perform the function of a working electrode. The working electrode can measure a limiting test current proportional to the reduced mediator concentration. For example, if the current limiting substance is a reduced mediator (e.g., potassium ferrocyanide), it can be oxidized at the first electrode 66 as long as the test voltage is sufficiently greater than the redox mediator potential relative to the second electrode 64. In this case, the first electrode 66 performs the function of the working electrode, and the second electrode 64 performs the function of the counter/reference electrode. The applicant has noted that the counter/reference electrode may simply be referred to as reference electrode or counter electrode. Limiting oxidation occurs when all of the reduced mediator at the working electrode surface has been depleted, such that the measured oxidation current is proportional to the flux of reduced mediator diffusing from the bulk solution toward the working electrode surface. The term "bulk solution" as used herein refers to the portion of the solution that is sufficiently far from the working electrode that the reduced mediator is not located in the depletion region. It should be noted that unless otherwise noted for the test strip 62, all potentials applied by the test meter 10 will be described below with respect to the second electrode 64.

Similarly, if the test voltage is sufficiently less than the redox mediator potential, the reduced mediator may be oxidized at the second electrode 64 as a limiting current. In this case, the second electrode 64 performs the function of the working electrode, and the first electrode 66 performs the function of the counter/reference electrode.

Initially, the analysis may include introducing a volume of the fluid sample into the sample-receiving chamber 61 via one of the ports 70. In one aspect, port 70 and/or sample-receiving chamber 61 may be configured such that capillary action causes the fluid sample to fill sample-receiving chamber 61. The first electrode 66 and/or the second electrode 64 may be coated with a hydrophilic reagent to promote capillary action of the sample-receiving chamber 61. For example, a thiol derivatizing reagent having a hydrophilic moiety (such as 2-mercaptoethanesulfonic acid) may be coated onto the first electrode and/or the second electrode.

In the analysis of test strip 62 described above, reagent layer 72 may include a PQQ co-factor and ferricyanide-based Glucose Dehydrogenase (GDH). In another example, PQQ cofactor-based enzyme GDH can be replaced with FAD cofactor-based enzyme GDH.When blood or control solution is dosed into sample reaction chamber 61, glucose is supplied by GDH_(ox)Oxidized and GDH is oxidized in the process_(ox)Conversion to GDH_(Red)As shown by chemical transformation t.1 below. Note that GDH_(ox)Refers to the oxidation state of GDH, and GDH_(Red)Refers to the reduced state of GDH.

T.1D-glucose + GDH_(ox)→ gluconic acid + GDH_(Red)。

Next, GDH_(Red)By ferricyanide (i.e. oxidation mediator or Fe (CN))₆ ^3-Such as potassium ferricyanide) is regenerated back to its active oxidation state, such as shown below by chemical transformation t.2. In regenerating GDH_(ox)In (2), ferrocyanide (i.e., a reducing mediator or Fe (CN))₆ ^4-Such as potassium ferrocyanide) from the reaction, as shown by t.2:

T.2 GDH_(Red)+2Fe(CN)₆ ^3-→GDH_(ox)+2Fe(CN)₆ ^4-。

Fig. 4 provides a simplified schematic diagram illustrating the test meter 10 engaged with the first and

second contact pads

67a, 67b, 63 of the test strip 62. The second contact pad 63 may be used to establish an electrical connection with the test meter 10 through the U-shaped recess 65, as shown in fig. 3B. In one embodiment, the test meter 10 may include a second electrode connector 101, a first electrode connector (102 a, 102 b), a test voltage unit 106, a current measurement unit 107, a processor 212, a memory unit 210, and a visual display 202, as schematically illustrated in FIG. 4. The first contact pad 67 may include two pins, indicated as 67a and 67 b. In one exemplary embodiment, the

first electrode connectors

102a and 102b are individually connected to the

pins

67a and 67b, respectively. The second electrode connector 101 may be connected to the second contact pad 63. The test meter 10 can measure the resistance or electrical continuity between the

pins

67a and 67b to determine whether the test strip 62 is electrically connected to the test meter 10.

In one embodiment, the test meter 10 may apply a test voltage and/or current between the first contact pad 67 and the second contact pad 63. Once the test meter 10 recognizes that the test strip 62 has been inserted, the test meter 10 is energized and initiates a fluid detection mode. In one embodiment, the fluid detection mode causes the test meter 10 to apply a constant current of approximately 1 microampere between the first electrode 66 and the second electrode 64. Because the test strip 62 is initially dry, the test meter 10 measures a relatively large voltage. When the fluid sample bridges the gap between the first electrode 66 and the second electrode 64 during the dosing process, the test meter 10 will measure a decrease in the measurement voltage below a predetermined threshold, causing the test meter 10 to automatically initiate a glucose test.

Referring to fig. 5A-5C, a method of determining an analyte concentration using the test strip 62 and test meter 10 will now be described. As an overview, first, the application of a test voltage and the measurement of a current value will be discussed, followed by an explanation of the analyte concentration measurement.

First, with respect to applying a voltage to a test strip, the example meter 10 and the example test strip 62 are references. The test meter 10 can include electronic circuitry that can be used to apply a plurality of voltages to the test strip 62 and measure the current transient output produced by the electrochemical reaction in the test chamber of the test strip 62. Test meter 10 may also include a signal processor having a set of instructions for a method of determining an analyte concentration in a fluid sample as disclosed herein. In one embodiment, the analyte is blood glucose.

Continuing with the discussion of the application of the test voltages, FIG. 5A presents an exemplary waveform consisting of a plurality of test voltages applied to the test strip 62 over a prescribed time interval. A plurality of test voltages according to the waveform are included at a first time interval t₁Internally applied first test voltage E1, at a second time interval t₂Internally applied second test voltage E2 and at a third time interval t₃Internal application of a third test voltage E3. The third voltage E3 may differ with respect to the second test voltage E2 in magnitude, polarity, or a combination of both of the electromotive forces. In a preferred embodiment and as shown, E3 may have the same amplitude as E2, but opposite polarity. Glucose test time interval t_GRepresents the amount of time (but not necessarily the same as) that the glucose test was performedAll calculations associated with glucose testing). Glucose test time interval t_GAnd may range from about 1.1 seconds to about 5 seconds. Furthermore, as shown in fig. 5A, the second test voltage E2 may include a constant (DC) test voltage component and a superimposed Alternating (AC) or alternatively oscillating test voltage component applied over a short time interval. More specifically, at the beginning of the second time interval, may be at t_capA superimposed alternating or oscillating test voltage component is applied for the indicated time interval.

The plurality of test current values measured during any time interval may be performed in a frequency range from about 1 measurement every microsecond to about 1 measurement every 100 milliseconds, and is preferably performed at about 50 milliseconds. Although an embodiment is described in which three test voltages are used in a serial fashion, the glucose test may include a different number of open circuits and test voltages. For example, as an alternative embodiment, the glucose test may include, for example, an open circuit for a first time interval, a second test voltage for a second time interval, and a third test voltage for a third time interval. It should be noted that references to "first," "second," and "third" are chosen for convenience and do not necessarily reflect the order in which the test voltages are applied. For example, embodiments may have a potential waveform in which a third test voltage may be applied before the first and second test voltages are applied.

Fig. 5C is a flow chart representing a method 500 for determining an analyte concentration in a nominal or uncontaminated test strip based on the waveform of fig. 5A and the measured current as shown in fig. 5B. In exemplary step 510, a glucose determination is initiated by inserting the test strip 62 into the test meter 10 and by depositing a sample on the test strip 62. In exemplary step 520, test meter 10 may be tested for a first time interval t₁A first test voltage E1 (e.g., approximately 20 mV in fig. 5A) is applied between first electrode 66 and second electrode 64 (e.g., 1 second in fig. 5A). First time interval t₁Can range from about 0.1 seconds to about 3 seconds, and preferably ranges from about 0.2 seconds to about 2 seconds, and most preferably from about 0.3 seconds to about 1.1 secondsWithin the range.

First time interval t₁May be long enough so that sample-receiving chamber 61 may be completely filled with sample, and also so that reagent layer 72 may be at least partially dissolved or solvated. In one aspect, the first test voltage E1 may be a value that is relatively close to the redox potential of the mediator, such that a relatively small amount of reduction or oxidation current is measured. FIG. 5B shows the second and third time intervals t₂And t₃In contrast, at a first time interval t₁During which a relatively small amount of current is observed. For example, when potassium ferricyanide and/or potassium ferrocyanide are used as mediators, first test voltage E1 in FIG. 5A can be in the range of from about 1 mV to about 100 mV, preferably in the range of from about 5 mV to about 50 mV, and most preferably in the range of from about 10 mV to about 30 mV. Although the applied voltage is given as a positive value in the preferred embodiment, the same voltage in the negative domain can also be used to achieve the intended purpose of the claimed invention. During the interval, the processor may sample the first current output to collect current values within the interval at step 530.

In exemplary step 540, after applying a first test voltage E1 (step 520) and sampling the output (step 530), test meter 10 samples for a second time interval t₂A second test voltage E2 (e.g., approximately 300 millivolts in fig. 5A) is applied between first electrode 66 and second electrode 64 (e.g., approximately 3 seconds in fig. 5A). The second test voltage E2 may be a value different from the first test voltage E1 and may be a sufficiently negative value for the mediator redox potential to measure the limiting oxidation current at the second electrode 64. For example, when potassium ferricyanide and/or potassium ferrocyanide are used as mediators, second test voltage E2 can range from about zero millivolts to about 600 millivolts, preferably from about 100 millivolts to about 600 millivolts, and more preferably about 300 millivolts.

Second time interval t₂Should be long enough so that the rate of generation of reduced mediator (e.g., potassium ferrocyanide) can be monitored based on the magnitude of the limiting oxidation current. The reduced mediator is generated by an enzymatic reaction with the reagent layer 72. At a second time interval t₂During this time, a limiting amount of the reduced mediator is oxidized at the second electrode 64, and a non-limiting amount of the oxidized mediator is reduced at the first electrode 66 to form a concentration gradient between the first electrode 66 and the second electrode 64.

In an exemplary embodiment, the second time interval t₂It should also be long enough so that a sufficient amount of potassium ferricyanide can diffuse to the second electrode 64 or from the reagent on the first electrode. A sufficient amount of potassium ferricyanide is required at the second electrode 64 so that the limiting current for potassium ferrocyanide oxide at the first electrode 66 can be measured during the third test voltage E3. Second time interval t₂May be less than about 60 seconds, and preferably may range from about 1.1 seconds to about 10 seconds, and more preferably ranges from about 2 seconds to about 5 seconds. Also, indicated as t in FIG. 5A_capThe time interval of (c) may also last a time range, but in an exemplary embodiment it has a duration of about 20 milliseconds. In one exemplary embodiment, the superimposed alternating test voltage component is applied after about 0.3 seconds to about 0.4 seconds after application of second test voltage E2, and induces a sine wave having a frequency of about 109 Hz and an amplitude of about +/-50 millivolts. During the interval, the processor may sample the second current output to collect current values within the interval at step 550.

FIG. 5B shows that at a second time interval t₂Relatively small peak i after onset_pbFollowed by a second time interval t₂During which the absolute value of the oxidation current gradually increases. After a transition from the first voltage E1 to the second voltage E2, a second time interval t is caused by the oxidation of endogenous or exogenous reducing agents₂During which the absolute value of the oxidation current gradually increases, so that a small peak i occurs_pb. Small peak value i_pbThis occurs due to the initial depletion of the reduced mediator after the transition from the first voltage E1 to the second voltage E2 (referred to herein as the transition line TL). Thereafter, the formation of potassium ferrocyanide in the reagent layer 72 results in a small peak i_pbThe oxidation current is then gradually reduced to absolute value, and potassium ferrocyanide then diffuses to the second electrodeAnd a pole 64.

In exemplary step 560, after applying a second test voltage E2 (step 540) and sampling the output (step 550), the test meter 10 is tested for a third time interval t₃A third test voltage E3 (e.g., about-300 millivolts in fig. 5A) is applied between first electrode 66 and second electrode 64 (e.g., 1 second in fig. 5A). The third test voltage E3 may be a value where the mediator redox potential is sufficiently positive such that a limiting oxidation current is measured at the first electrode 66. For example, when potassium ferricyanide and/or potassium ferrocyanide are used as mediators, the third test voltage E3 can range from about zero millivolts to about-600 millivolts, preferably from about-100 millivolts to about-600 millivolts, and more preferably about-300 millivolts.

After applying the third test voltage E3, in step 570, for a third time interval t₃The current value is measured. Third time interval t₃Can be long enough to monitor the diffusion of the reduced mediator (e.g., potassium ferrocyanide) near the first electrode 66 based on the magnitude of the oxidation current. At a third time interval t₃During this time, a limited amount of the reduced mediator is oxidized at the first electrode 66, and a non-limiting amount of the oxidized mediator is reduced at the second electrode 64. Third time interval t₃May be in the range of from about 0.1 seconds to about 5 seconds, and preferably in the range of from about 0.3 seconds to about 3 seconds, and more preferably in the range of from about 0.5 seconds to about 2 seconds.

FIG. 5B shows that for a nominal test strip, at a third time interval t₃Relatively large peak i at the beginning_pcThen decreases to the steady-state current i_ssThe value is obtained. In one embodiment, the second test voltage E2 may have a first polarity and the third test voltage E3 may have a second polarity opposite the first polarity. In another embodiment, the second test voltage E2 may be sufficiently negative for the redox potential of the mediator, and the third test voltage E3 may be sufficiently positive for the redox potential of the mediator. The third test voltage E3 may be applied immediately after the second test voltage E2. However, those skilled in the art will appreciate that the magnitudes and polarities of the second and third test voltagesThe properties may be selected depending on the manner in which the analyte concentration is determined.

Next, glucose concentration determination is described for embodiments described herein, and as set forth in step 580 of fig. 5C. Fig. 5A and 5B show a sequence of events in a test strip transient. At approximately 1.1 seconds after the start of the test sequence (and shortly after the second electrode becomes the working electrode due to the application of the second voltage E2), a current measurement is taken to later correct for the disturbance when no reagent has yet reached the first electrode and the current may be due only to the interfering reducing agent in the plasma (in the absence of mediator). Between about 1.4 seconds and about 4 seconds, the first glucose proportional current i is measured when (at least in the second half of the interval during which the second voltage E2 is applied) the mediator and the oxidized mediator have been able to diffuse to the second electrode_l. Shortly after the first electrode is made the working electrode by applying the third voltage E3, 2 single-point measurements (at approximately 4.1 and 5 seconds according to this example) and one integral measurement i are taken_r. According to this particular embodiment, the measured values sampled at 1.1, 4.1 and 5 seconds, respectively, are used to correct i for the additional current from the interfering reducing agent_r（i2corr）。i_lAnd i_rIs used for the correction of the interference effects against hematocriti2corr。

In one embodiment, the glucose concentration is then determined using the following equation:

wherein:

G _basicis the analyte concentration;

i _ris the sum of the third current values during the third time interval;

i _lis the sum of the second current values during the second time interval;

(ii) a And

a. b, p and z_grIs a predetermined coefficient.

In one particular example of the use of the invention,

。

in another example, different test strip chemistries may be used, with the times that occur in the current evaluation varying according to the general relationship described above. Additional details regarding the applied waveform and determination of the analyte concentration of the test strip are provided in U.S. patent No. 8,709,232 (B2) and international patent publication No. WO 2012/012341 a1, which are incorporated herein by reference.

As described above, fig. 6A describes in detail an enlarged partial view of the current versus time based on the waveform of fig. 5A. In this figure, the current response of fig. 5B is reproduced for a nominal (uncontaminated) test strip, such as test strip 62 of fig. 1, as compared to the current response of a moisture-contaminated test strip. As clearly shown in this figure, there are a number of characteristic anomalies between the nominal test strip and the anomaly/defective test strip during part of the current transient. More specifically, the contaminated test strip includes a plurality of spike current transients exhibited between approximately 0 and 1 second (during a predetermined first time interval). In addition, the contaminated test strip exhibits a reduced peak i after application of the test voltage at the beginning of a second time interval at about 1 second after the start of the test sequence_pb。

Without being bound by any particular theory, the physical mechanism of moisture contamination appears to be the introduction of moisture (from storage conditions or other reasons) resulting in the conversion of potassium ferricyanide to potassium ferrocyanide in the test strip reagent layer. In this case, the reagent layer has a relatively high concentration of potassium ferrocyanide, which can diffuse and be consumed at both the first and second electrode surfaces during analyte concentration measurement. Thus, when the test strip is contaminated, the analyte signal will be amplified, resulting in a higher than expected glucose measurement.

As described in the later section, it was experimentally verified that in the first and second time intervals of the test waveform, there were many discrete and identifiable anomalies attributable to the effects of contamination (moisture). These effects are illustrated in comparison in fig. 6A. This contamination is characterized by both physical and chemical changes to the test strip. For example, the physical change occurs because a test strip including an electrode coated with a uniform dielectric layer prior to contamination or damage may now effectively exhibit a rough or inconsistent layer of unconverted dielectric. In this case, when a blood sample is applied to the test strip, a transient current such as that observed in the first time interval may be generated due to the non-uniformity of this layer of the test strip.

In addition, the test strip may also undergo chemical changes. These chemical changes may be due to the total amount of mediator that has been converted resulting in a tangible and perceptible change in the expected current response of the test strip at the applied voltage, and more specifically the second test voltage. Combinations of physical and chemical changes to a contaminated or damaged test strip have been generally described, but the techniques for determining contamination are not limited by any particular aspect of the present discussion.

Due to the perceptible difference between the expected current response of a nominal test strip and the current response exhibited by a contaminated test strip, a number of reference values labeled a-E according to fig. 6A may be cited for convenience when the test strip is inserted into a portable test meter for analyte measurement purposes. According to one embodiment, identification of particular aspects of an abnormal current response that have been determined (depicted as reference values A, B and C) may be sufficient to determine the presence of a contaminated test strip.

According to one embodiment, the reference value a is the sum of the current values measured during a first time interval (for example between 0.20 and 0.75 seconds). As described above, the contaminated test strip exhibits a physical change that results in a greater current response in the first time interval, as the dielectric layer becomes physically less uniform. The sum of the current values during the first time interval is therefore indicative of the magnitude of these physical changes to the test strip due to contamination and is used as the reference value a. In one particular example, the contaminated test strip exhibits a sum of current values between 0.20 and 0.75 seconds in an amount greater than 6.5 μ Α.

As described above, the contaminated test strip exhibited a smaller peak current i at 1.0 second_bcThis is caused by chemical changes in the test strip due to contamination. This contamination causes a deviation in the peak current. In one specific example, if the measured peak current value i during the second time interval_bcLess than 12.5 muA indicates a chemical change consistent with contamination and the peak represents the reference value B.

Furthermore, the chemical change also results in a slow negative rate of change of the measured current after the peak current. Thus, if the peak is at 1.05 seconds, the difference in value between 1.10 seconds and 1.05 seconds is a measure of this rate of change, which is referred to herein as the reference value C. Thus, the test strip can be further characterized by a reference value C, which is the difference between the current value at 1.10 seconds and the current value at 1.05 seconds. In one particular example, the difference may be between 0 and-3.5 μ Α. In another example, the difference may be divided by the time difference of the two values (e.g., 1.10 seconds-1.05 seconds = 0.05 seconds) to give the time rate of change of the current. Referring to fig. 6B, reference values B and C may be determined at step 660.

In one embodiment, reference values B and C may be used in conjunction with reference value a to determine contamination of the test strip, such as at step 670 of fig. 6B. After determining that the test strip is contaminated, at step 670 of fig. 6, the meter may display or annunciate a message indicating that the test strip is contaminated. Advantageously, the determination of contamination of the test strip allows education to the user of the test meter. The user may be provided with information that educates the user about the proper storage of the test strip, including the need to store the test strip in a sealed container provided and away from extreme heat and light.

In one embodiment, where the above-described indicia is used to determine the contamination of a particular test strip, the test measurement system may invalidate the test results from the contaminated biosensor and a new biosensor should be loaded for testing. Also, if the new biosensor does not exhibit the waveform characteristics associated with contamination, the test measurement system may notify the patient of the test results. In other embodiments, insulin may be automatically delivered to the patient only when the biosensor is not contaminated (as determined by the techniques described above).

In another embodiment, a further improvement utilizes the observation that a contaminated test strip is characterized as having a greater range of current values during the first interval than a nominal test strip. Specifically, the range is defined as the difference between the maximum current value and the minimum current value of the transient current exhibited in the contaminated test strip in the first time interval. Thus, the reference value D is defined as the difference between the maximum current value and the minimum current value during the first time interval. In one particular example, the range of the difference (i.e., the reference value D) is greater than 0.57 μ a for contaminated test strips and less than 0.57 μ a for nominal test strips.

In another embodiment, another improvement eliminates false positive contamination determinations by checking whether a contaminated test strip exhibits a current during testing that is consistent with the movement of the test strip within the meter. For example, during the testing process, movement of the finger against the test strip may result in some current deviation. Thus, a reference value E may be defined, i.e. the minimum value of the current in the first time interval is larger than 0 μ a. Referring to fig. 6B, reference values A, D and E may be determined at step 640.

Given the definition of the reference values A-E, a set of markers (indicia) can be defined for purposes of the analyte measurement system based on the perceptible and representative differences between the nominal test strip (FIGS. 5B and 6A) and the exception test strip (FIG. 6A)_A-marking_F). Each flag is a boolean flag, which may be true or false, and each flag a-E is based on comparing a respective reference value a-E with a respective range or value defined by a respective target value a-E.

If the reference value A is greater than the target value A, marking_ATo be true, the reference value A is defined as being part of a first time interval(e.g., between 0.20 and 0.75 seconds). In this specific example, the target value a is 6.5 μ a. However, it has been determined that a target value a in the range of 5-10 μ a provides sufficient efficacy.

If the reference value B is less than about the target value B, marking_BTo be true, the reference value B is defined as the peak current value i measured during the second time interval_pb. In this specific example, the target value B is 12.5 μ a. However, it has been determined that a target value B in the range of 12-12.5 μ a provides sufficient efficacy for identifying abnormal test strips.

If the reference value C is between 0 and the target value C, marking_CTo be true, the reference value C is defined as the measured peak current value i_pb(e.g., at 1.05 seconds) and the current value at 1.10 seconds. In this specific example, the target value C is-3.5 μ Α. However, it has been determined that a target value C in the range of approximately 0- — 4.5 μ A provides sufficient efficacy for identifying contaminated test strips.

If the reference value D is greater than about the target value D, marking_DThe reference value D is defined as the difference between the maximum current value and the minimum current value in the first time interval, which is true. It has been determined that a target value D in the range of approximately 0.4-0.65 mua provides sufficient efficacy. According to this specific example, the target value D is 0.57 μ a.

Finally, if the reference value E is greater than about the target value E, the flag is asserted_ETo be true, the reference value E is defined as the minimum transient current in the first time interval, such as about 0A in this particular example.

In one embodiment, when marking_A-marking_EWhen one or more of them evaluates to true, e.g. only the token_AAnd a label_BAnd a mark_CContamination or damage to the test strip can be determined. In another embodiment, when all the marks are present_A-marking_EWhen the evaluation is true, contamination or damage to the test strip can be determined. For example, markers A, D and E can be considered to represent physical changes due to contamination as described above, and markers B and C can be considered to represent contamination due to the aboveChemical changes caused by said contamination. In this case, the combination of at least one marker from each set (i.e., one of markers A, D and E and one of markers B and C) can be used to determine contamination by a combination of physical and chemical changes of the test strip.

More notably, markers A, D and E occur earlier in the test sequence than markers B and C, and thus may be more susceptible to false positives due to blood filling issues with the finger or movement/nudging of the test strip during testing. As an advantage, the present technology can combine the markers from each set to eliminate such false positives so that uncontaminated test strips are not wasted due to these false positives. In addition, the selection of target values a-E within the above ranges advantageously provides a balance between the desired results of capturing as many true positives as possible while avoiding as many false positives as possible.

Unexpectedly, during testing of test strips that were intentionally exposed to moisture, various deviations in the output waveform occurred, including the transient current values, as described above with reference to fig. 6A. For example, although some potential proven changes may be experienced based on applying the sample from a fingertip rather than a pipette due to changes in fill rate, changes in current response relative to the nominal current response of fig. 5B due to physical property changes in the reagent layer may also be observed, as described above.

To verify the authenticity of the technique, 92 contaminated test strips were tested. The test strip is determined to be contaminated because the test strip is stored in a container containing a desiccant, and the desiccant is inspected and found to contain moisture. The test meter is used to apply a voltage to the test strip and capture the output current as described herein. First, conventional techniques for detecting test errors are applied to the captured current, and a total of 39 contaminated test strips are identified as having errors related to other factors, such as fill, etc. When applying the present technique to captured transients, all 92 contaminated test strips were correctly identified based on the above reference values using the combination of markers A, B, C, D and E.

While the invention has been described in terms of particular variations and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the variations or figures described. Additionally, where methods and steps described above indicate specific events occurring in a specific order, those of ordinary skill in the art will recognize that the order of the specific steps may be modified and that such modifications are in accordance with the variations of the present invention. Additionally, certain steps may be performed concurrently in a parallel process when possible, or may be performed sequentially as described above. Thus, to the extent that modifications of the invention are included within the spirit of the disclosure or equivalent to the inventions found in the claims, it is the intent of this patent to cover those modifications as well.

To the extent that the claim recites the phrase "at least one" to a plurality of elements, it is intended to mean at least one or more of the elements listed, and not limited to at least one of each element. For example, "at least one of element a, element B, and element C" is intended to indicate either element a alone, or element B alone, or element C alone, or any combination thereof. "at least one of element a, element B, and element C" is not intended to be limited to at least one of element a, element B, and element C.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they are intended to have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" (and any form of comprising, such as "comprises" and "comprising)", "has" (and any form of having, such as "has" and "has)", "contains" (and any form of containing, such as "contains" and "containing)") and "contains" (and any form of containing, such as "contains" and "containing)") are open-ended linking verbs. Thus, a method or apparatus that "comprises," "has," "includes" or "contains" one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that "comprises," "has," "includes" or "contains" one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Further, a device or structure configured in a certain way is configured in at least that way, but may also be configured in ways not listed.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description as set forth herein is presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of one or more aspects set forth herein and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects described herein for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

1. A method for determining the presence of biosensor contamination, the method comprising:

loading the biosensor into a test meter and applying a sample to the biosensor, the biosensor having an electrochemical cell defined by a pair of spaced electrodes;

applying a first predetermined voltage between spaced electrodes of said electrochemical cell for a first predetermined time interval and applying a second predetermined voltage between said spaced electrodes during a second predetermined time interval after said first predetermined time interval;

measuring a first current value during the first predetermined time interval;

determining a first reference value based on a sum of first current values during the first predetermined time interval;

measuring a second current value during the second predetermined time interval;

determining a second reference value based on the peak current value measured during the second predetermined time interval and determining a third reference value based on a rate of change of the current value measured after the peak current value during the second time interval;

determining whether the biosensor is contaminated based on one or more of the first to third reference values; and

inhibiting reporting of an analyte concentration upon determining that the biosensor is contaminated based on one or more of the first through third reference values.

2. The method of claim 1, wherein determining that the biosensor is contaminated is based on all of the first to third reference values.

3. The method of claim 1, wherein the first reference value comprises a sum of first current values between about 0.2 seconds and 0.75 seconds after applying the first predetermined voltage, and determining that the biosensor is contaminated is based on the first reference value being greater than about 6.5 μ A.

4. The method of claim 1, wherein the second reference value is based on a peak current value measured during a second predetermined time interval of less than about 12.5 μ A.

5. The method of claim 4, wherein the peak current value is measured at about 0.05 seconds after the second predetermined voltage is applied.

6. The method of claim 1, wherein the third reference value comprises a difference between a current value measured at about 0.1 seconds after applying the second predetermined voltage and a peak current value measured during the second predetermined time interval, and the determining that the biosensor is contaminated is between about-3.5 μ Α and 0 μ Α based on the third reference value.

7. The method of claim 1, further comprising determining a fourth reference value based on a magnitude of a difference between a highest measured current value and a lowest measured current value during the first predetermined time interval, and determining that the biosensor is contaminated is further based on the fourth reference value.

8. The method according to claim 7, wherein the fourth reference value comprises a magnitude of a difference between a highest measured current value and a lowest measured current value between about 0.2 seconds and 0.75 seconds after applying the first predetermined voltage, and determining that the biosensor is contaminated based on the measured second reference value being greater than about 0.57 μ A.

9. The method of claim 1, further comprising determining a fifth reference value based on a minimum measured current value during the first predetermined time interval, and determining that the biosensor is contaminated is further based on the fifth reference value.

10. The method of claim 9, wherein the fifth reference value comprises a minimum value of a current value between about 0.2 seconds and 0.75 seconds after applying the first predetermined voltage, and the biosensor is determined to be contaminated based on the fifth reference value being greater than about 0 μ Α.

11. The method of claim 1, further comprising calculating a concentration of the analyte based on the second current value and a third current value measured in a third predetermined time interval.

12. The method of claim 11, wherein calculating an analyte concentration comprises using an equation of the form, wherein:

wherein:

G _basicis the analyte concentration;

i _ris the sum of the third current values during the third time interval;

i _lis the sum of the second current values during the second time interval;

(ii) a And is

a. b, p and z_grIs a predetermined coefficient.

13. A test meter for determining the presence of contamination of a biosensor, the test meter comprising:

a voltage source;

a user interface; and

a controller configured to:

applying a first predetermined voltage between spaced electrodes of said electrochemical cell with a voltage source for a first predetermined time interval;

measuring a first current value during the first predetermined time interval;

determining a first reference value based on a sum of the first current values during the first predetermined time interval;

applying a second predetermined voltage between said spaced electrodes with a voltage source during a second predetermined time interval after said first predetermined time interval;

measuring a second current value during the second predetermined time interval;

determining a second reference value based on a peak current value measured during the second predetermined time interval and determining a third reference value based on a rate of change of a current value measured after the peak current value during the second time interval; and

displaying on the user interface whether the biosensor is contaminated based on one or more of the first to third reference values.

14. The test meter of claim 13, wherein the test meter is further configured to calculate a concentration of the analyte based on the second current value and the third current value.

15. The test meter of claim 14, wherein calculating an analyte concentration comprises using an equation of the form:

wherein:

G _basicis the analyte concentration;

i _ris the sum of the third current values during the third time interval;

i _lis the sum of the second current values during the second time interval;

(ii) a And is

a. b, p and z_grIs a predetermined coefficient.

16. The test meter of claim 13, wherein determining that the biosensor is contaminated is based on all of the first to third reference values.

17. The test meter of claim 13, wherein the first reference value comprises a sum of first current values between approximately 0.2 seconds and 0.75 seconds after applying the first predetermined voltage, and determining that the biosensor is contaminated is based on the first reference value being greater than approximately 6.5 μ Α.

18. The test meter of claim 13, wherein the second reference value is based on a peak current value measured during the second predetermined time interval of less than about 12.5.

19. The test meter of claim 13, wherein the third reference value comprises a difference between a current value measured at about 0.1 seconds after applying the second predetermined voltage and a peak current value measured during the second predetermined time interval, and the determination that the biosensor is contaminated is based on the third reference value being between about-3.5 μ Α and 0 μ Α.