Error detection in analyte measurements based on measurement of system resistance

• US 7,846,321 B2
• Filed: 10/18/2007
• Issued: 12/07/2010
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Original Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Inventors: Diamond, Steven, Harding, Ian, Williams, Richard
• Primary Examiner(s): Nguyen; Nam X
• Assistant Examiner(s): LEONG, SUSAN DANG
• Application Number:
  US11/874,766
• Publication Number:
  US 20080093227A1
• Time in Patent Office: 1,146 Days
• Field of Search: 435 4- 4052, 4352871-2887, 324691-724, 702 19- 26, 702 85-107, 205/777.5, 205/778, 205/792, 600345-348, 422 681- 98, 436 62- 71, 436500-548, 20440301-40315
• US Class Current: 205/778
• 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

Measurement of the series track resistance of a working and counter electrode pair in an electrochemical test strip provide error detection for multiple variations in the quality of the test strip, as well as the operation of strip in the test meter. In particular, a single measurement of series resistance can be used to detect and generate an error message when an incorrect reading is likely to result due to (1) damaged electrode tracks, (2) fouled electrode surfaces, (3) dirty strip contacts, or (4) short circuit between the electrodes.

Claims

1. A method for determination of an analyte in a sample comprising the steps of:

(a) introducing the sample to an electrochemical test strip having working and counter electrodes;

(b) applying a potential difference, V_app, between the electrodes of the test strip and observing a current signal sufficient to provide a determination of analyte in the sample and for a period of time sufficient to determine a plateau current, I_plateau, that reflects the recycling or shuttling of mediator between the electrodes;

(c) switching off the applied potential at time t_switch and determining the magnitude, V_drop, of a voltage drop arising from series electrode resistance, if present;

(d) calculating a track resistance R_track, and comparing the determined magnitude of R_track against a predetermined range, and rejecting the test if the magnitude of R_track falls outside of the range wherein the value of R_track=V_drop/I_plateau, and

(e) if the magnitude is within the predetermined range, proceeding to display or communicate the result from the determination of analyte.

2. The method of claim 1, wherein V_drop is defined as the difference in potential between V_app and the potential measured at a predetermined time after the potential is switched off .

3. The method of claim 1, wherein V_drop is defined as the difference in potential between V _app and the electrochemical potential, V_elect.

4. The method of claim 3, wherein V_elect is determined by extrapolating voltage decay observed in a time interval after the potential is switched off when decrease in potential associated with series electrode resistance has occurred and determining the extrapolated value of potential at the time the potential was switched off.

5. The method of claim 4, wherein the time interval is from 0.5 to 2 milliseconds.

6. The method of claim 5, wherein the time interval is 1 millisecond.

7. A meter for receiving an electrochemical test strip having working and counter electrodes and providing a determination of an analyte in a sample applied to the electrochemical test strip when received in the meter, said meter comprising

(a) a housing having a slot for receiving an electrochemical test strip;

(b) communications means for receiving input from and communicating a result to a user; and

(c) means for applying a potential and to determine analyte concentration from an observed current and for measuring a plateau current, I_plateau,

(d) means for switching off the potential at time t_switch and determining V_drop;

(e) means for calculating R_track; and

(f) means for comparing R_track with a predetermined range and generating an error message in place of a result if R_track falls outside the range.

8. The meter of claim 7, wherein V_drop is defined as the difference in potential between V_app and the potential measured at a predetermined time after the potential is switched off.

9. The meter of claim 7, wherein V_drop is defined as the difference between in potential between V_app and the electrochemical potential, V_elect.

10. The meter of claim 9, wherein V_elect, is determined by extrapolating voltage decay observed in a time interval after the potential is switched off when decrease in potential associated with series electrode resistance has occurred and determining the extrapolated value of potential at time t_switch.