Method for determining hematocrit corrected analyte concentrations

• US 8,388,821 B2
• Filed: 10/05/2007
• Issued: 03/05/2013
• Est. Priority Date: 10/05/2006
• Status: Expired due to Fees

• Current Assignee: Cilag Gmbh International (Johnson & Johnson)
• Original Assignee: LifeScan Scotland Limited (Johnson & Johnson)
• Inventors: Cardosi, Marco F., Gill, Andrew, Mills, Leanne, Leach, Christopher Philip, Blythe, Stephen Patrick
• Primary Examiner(s): Ball, J. Christopher
• Application Number:
  US12/305,363
• Publication Number:
  US 20100219084A1
• Time in Patent Office: 1,978 Days
• Field of Search: 205/775, 205/777.5, 205/778, 205/792, 20440301-40315, 435/4, 435/14, 435 25- 28, 600/345, 600/347
• US Class Current: 204/403.02
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: G01N 27/3271 Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood amperometry per se G01N27/49; aspects concerning the enzyme reagent C12Q1/001

Abstract

Description is provided herein for an embodiment of a method determining a hematocrit-corrected glucose concentration. The exemplary method includes providing a test strip having a reference electrode and a working electrode, wherein the working electrode includes a plurality of microelectrodes and is coated with at least an enzyme and a mediator. The method can be achieved by: providing a test strip comprising a reference electrode and a working electrode formed with a plurality of microelectrodes and coated with a reagent layer; applying a fluid sample to the test strip for a reaction period; applying a test voltage between the reference electrode and the working electrode; measuring a test current as a function of time; measuring a steady state current value when the test current has reached an equilibrium; calculating a ratio of the test current to the steady state current value; plotting the ratio of the test current to the steady state current value as a function of the inverse square root of time; calculating an effective diffusion coefficient from the slope of the linearly regressed plot of the ratio of the test current to the steady state current value as a function of the inverse square root of time; and calculating a hematocrit-corrected concentration of analyte.

Claims

1. A method of determining a type of fluid sample applied to the test strip, the method comprising:

providing a test strip having a reference electrode and a working electrode, wherein the working electrode is formed with a plurality of microelectrodes and is coated with a reagent layer;

applying a fluid sample to the test strip for a reaction period;

applying a test voltage between the reference electrode and the working electrode;

measuring a test current as a function of time;

measuring a steady state current value when the test current has reached an equilibrium;

calculating a ratio of the test current to the steady state current value;

plotting the ratio of the test current to the steady state current value as a function of the inverse square root of time;

calculating an effective diffusion coefficient from the slope of the linearly regressed plot of the ratio of the test current to the steady state current value as a function of the inverse square root of time;

determining a type of a fluid sample applied to the test strip by comparing a measured value for the effective diffusion coefficient against an acceptance range for a bodily fluid and a control solution; and

displaying an appropriate error message if the effective diffusion coefficient does not pass the acceptance range for the type of fluid sample applied to the test strip.

2. The method of claim 1, wherein the calculating of the effective diffusion coefficient step utilizes an equation of the form:

3. The method of claim 2, wherein the calculating a hematocrit-corrected concentration of analyte step further comprises:

substituting the estimated diffusion coefficient into an equation of the form;

4. The method of claim 1, wherein the test strip further comprises an insulation portion disposed on the plurality of microelectrodes and the insulation portion has a height between about one micron and about six microns.

5. The method of claim 1, wherein the reference electrode and the working electrode are comprised of gold.

6. The method of claim 1, wherein the reagent layer comprises an enzyme, a mediator and a buffering agent wherein the mediator comprises ruthenium (III) hexamine.

7. The method of claim 1, wherein the diameter of each of the plurality of microlectrodes is between about 5 microns and about 50 microns.

8. The method of claim 1, wherein each of the plurality of microelectrodes is spaced apart by a distance ranging from about 5 to about 10 times the diameter of a microelectrode.

9. The method of claim 1, wherein each of the plurality of microelectrodes is spaced apart by a distance ranging from about 25 microns to about 500 microns.

10. The method of claim 1, wherein the shape of each of the plurality of microelectrodes is selected from a group consisting of a circle, a square, a rectangle, an oval and an ellipse.

11. A system comprising:

a test strip having a reference electrode and a working electrode, wherein the working electrode formed with a plurality of microelectrodes and coated with an reagent layer and wherein the test strip further comprises an insulation portion disposed on the plurality of microelectrodes; and

a test meter comprising;

an electronic circuit for applying a test voltage between the reference electrode and the working electrode; and

a signal processor for measuring a test current and for calculating an effective diffusion coefficient.

12. The system of claim 11, wherein the insulation portion has a height between about one micron and about six microns.

13. The system of claim 11, wherein the effective diffusion coefficient is calculated from the slope of the linearly

14. The system of claim 13, wherein a hematocrit-corrected glucose concentration is calculated by using the estimated diffusion coefficient and an equation of the form:

15. The system of claim 11, wherein an effective diffusion coefficient is used to discriminate between a fluid sample of whole blood and a fluid sample of control solution by comparing the effective diffusion coefficient to an acceptance range for whole blood and an acceptance range for control solution and the effective diffusion coefficient is used to determine if a test strip is formed with a plurality of microelectrodes by substituting the effective diffusion coefficient into an equation of the form: