SYSTEM AND METHOD FOR MEASURING AN ANALYTE IN A SAMPLE

• US 20090301899A1
• Filed: 05/13/2009
• Published: 12/10/2009
• Est. Priority Date: 06/09/2008
• Status: Active Grant

• Current Assignee: Cilag Gmbh International (Johnson & Johnson)
• Original Assignee: Lifescan Incorporated (Duv Holding Corporation)
• Inventors: Chatelier, Ronald C., Hodges, Alastair M.
• Granted Patent: US 8,551,320 B2
• Time in Patent Office: Days
• US Class Current: 205/777.500
• CPC Class Codes: G01N 27/3274 Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771

Abstract

Methods for calculating an analyte concentration of a sample are provided. In one exemplary embodiment the method includes steps that are directed toward accounting for inaccuracies that occur as a result of temperature variations in a sample, a meter, or the surrounding environment. In another exemplary embodiment the method includes steps that are directed toward determining whether an adequate sample is provided in a meter because insufficient samples can result in inaccuracies. The methods that are provided can be incorporated into a variety of mechanisms, but they are primarily directed toward glucose meters for blood samples and toward meters for controls solutions.

Claims

1. A method for measuring a temperature corrected glucose concentration over a temperature range, the method comprising:

applying a sample to a test strip;

applying a first test voltage for a first time interval between a first electrode and a second electrode sufficient to oxidize a reduced mediator at the second electrode;

following the application of the first test voltage, applying a second test voltage for a second time interval between the first electrode and the second electrode sufficient to oxidize the reduced mediator at the first electrode

calculating a first glucose concentration based on test current values during the first time interval and the second time interval;

measuring a temperature value; and

calculating a temperature corrected glucose concentration based on the first glucose concentration and the temperature value.

2. The method of claim 1, in which the step of calculating the temperature corrected concentration comprises:

calculating a correction value based on the temperature value and the first glucose concentration;

calculating a temperature corrected concentration based on the first glucose concentration and the correction value.

3. The method of claim 2, in which the correction value is calculated with a first function if the temperature value is greater than a first temperature threshold.

4. The method of claim 2, in which the correction value is calculated with a second function if the temperature value is not greater than a first temperature threshold.

5. The method of claim 3, in which the first function is a first equation, the first equation being:

Corr₂=−

K₁(T−

T_RT)+K₂×

G₁(T−

T_RT)

where Corr₂ is the correction value, K₁ is a first constant, T is a temperature value, T_RT is a room temperature value, K₂ is a second constant, and G₁ is the first glucose concentration.

6. The method of claim 4, in which the second function is a second equation, the second equation being:

Corr₂=−

K₃(T−

T_RT)−

K₄×

G₁(T−

T_RT)−

K₅×

G₁(T−

T₁)+K₆×

G₁(T−

T₁)

where Corr₂ is the correction value, K₃ is a third constant, T is a temperature value, T_RT is a room temperature value, K₄ is a fourth constant, G₁ is a first glucose concentration, K₅ is a fifth constant, T₁ is a first temperature threshold, and K₆ is a sixth constant.

7. The method of claim 5 or 6, in which the step of calculating the temperature corrected concentration further comprises:

adding the correction value to the first glucose concentration to give the temperature corrected concentration if the first glucose concentration is less than a glucose threshold.

8. The method of claim 5 or 6, in which the step of calculating the temperature corrected concentration further comprises:

dividing the correction value by one hundred and adding one to give an intermediate term; and

multiplying the intermediate term times the first glucose concentration to give a temperature corrected concentration.

9. The method of claim 5 or 6 that further comprises the following step,

determining if the correction value is greater than a threshold value, then setting the correction value to the threshold value, where the threshold value is about ten.

10. The method of claim 2, in which the correction value is about zero when the temperature value is about equal to a room temperature value.

11. The method of claim 10, in which the room temperature value is about 22 degrees Celsius.

12. The method of claim 2, further comprises

determining whether the applied sample is a control solution;

and

calculating the correction value with a third function if the applied sample is control solution.

13. The method of claim 12, in which the third function is a third equation, the third equation being:

Corr₂=−

K₇(T−

T_RT)+K₈33 G₁(T−

T_RT)

where Corr₂ is the correction value, K₇ is a seventh constant, T is a temperature value, T_RT is a room temperature value, K₈ is an eighth constant, and G₁ is the first glucose concentration.

14. A method for determining whether a test strip is sufficiently filled with a sample, the method comprising:

applying a first test voltage between a first electrode and a second electrode of a test strip, the first test voltage having an AC voltage component and a DC voltage component, the AC voltage component being applied at a predetermined amount of time after the application of the first test voltage, the DC voltage component having a magnitude sufficient to cause a limiting test current at the second electrode, the second electrode not having a reagent layer coating; and

processing a portion of the test currents, resulting from the AC voltage component, into a capacitance value.

15. The method of claim 14, in which the predetermined amount of time ranges from about 0.3 seconds to about 0.4 seconds after the application of the first test voltage.

16. The method of claim 14, in which the predetermined amount of time is a time where a test current transient as a function of time has a slope of about zero.

17. The method of claim 14, in which the predetermined amount of time is a time required for a peak current value to decay by about 50%.

18. The method of claim 14, in which the limiting test current is a limiting oxidation test current where substantially all of a reduced mediator has been depleted at a surface of the second working electrode.

19. The method of claim 14, in which a magnitude of the first test voltage is sufficient to oxidize a reduced mediator at the second electrode.

20. The method of claim 14, in which the DC voltage component is applied at a beginning of the first test voltage.

21. The method of claim 14, in which the DC voltage component is about −

0.3 volts with respect to the second electrode.

22. The method of claim 14, in which the AC voltage component is a sine wave having a frequency of about 109 Hertz and an amplitude of about ±

50 millivolts.

23. The method of claim 14, in which the reagent layer coating is on the first electrode.

24. The method of claim 23, in which the reagent layer is configured to generate reduced mediator in a presence of an analyte.

25. The method of claim 24, in which the reagent layer comprises a mediator and an enzyme where the enzyme does not substantially diffuse from the first electrode to the second electrode when sample is introduced into the test strip.

26. The method of claim 14, in which the first electrode and the second electrode are in an opposing face format.

27. The method of claim 14, further comprising:

determining that the test strip is sufficiently filled with the sample if the capacitance value is greater than a predetermined threshold.

28. The method of claim 14, further comprising:

determining that the test strip is not sufficiently filled with the sample if the capacitance is less than a predetermined threshold.

29. The method of claim 14, in which a portion of the test currents, resulting from the AC voltage component and the DC voltage component, are summed between at about a ¼

wavelength before and about a ¼

wavelength after a zero voltage crossing point.

30. The method of claim 14, in which a portion of the test currents, resulting from the AC voltage component and the DC voltage component, are summed between at about a ¼

wavelength before and about a ¼

wavelength after about a maximum AC component.