Systems and methods for determining a substantially hematocrit independent analyte concentration
View Patent ↗A method and system is provided to allow for determination of substantially Hematocrit independent analyte concentration. In one example, an analyte measurement system is provided that includes a test strip and a test meter. The test strip includes a reference electrode and a working electrode, in which the working electrode is coated with a reagent layer. The test meter includes an electronic circuit and a signal processor. The electronic circuit applies a plurality of voltages to the reference electrode and the working electrode over respective durations. The signal processor is configured to determine a substantially hematocrit-independent concentration of the analyte from a plurality of current values as measured by the processor upon application of a plurality of test voltages to the reference and working electrodes over a plurality of durations interspersed with rest voltages lower than the test voltages being applied to the electrodes.
1. A method of detecting the presence of sufficient quantity of a fluid sample deposited on a test strip having a reference electrode and a working electrode, in which the working electrode is coated with a reagent layer, the method comprising:
applying a forward test voltage between the reference electrode and the working electrode and measuring a forward current value near the end of the forward test voltage, in which the forward test voltage is from about 100 millivolts to about 600 millivolts;
applying a reverse test voltage of opposite polarity and substantially equal magnitude to the forward test voltage between the reference electrode and the working electrode and measuring a reverse current value near the end of the reverse test voltage, the reverse test voltage being from about negative 100 millivolts to about negative 600 millivolts;
calculating a ratio of the reverse current value to the forward current value; and
determining if the ratio of the reverse current value to the forward current value is within an acceptance range, the acceptance range being substantially equal to two when the reference electrode is about twice the surface area of the working electrode; and
detecting the presence of sufficient quantity of the fluid sample based on the ratio.
2. The method of claim 1 , in which the duration of the forward test voltage ranges from about 0.1 to about 1.0 seconds; the magnitude of the forward test voltage is about 400 millivolts;
the forward current value is measured at about 0.1 to about 1.0 seconds after the forward test voltage is applied to the test strip; the duration of the reverse test voltage ranges from about 0.1 to about 1.0 seconds; the magnitude of the reverse test voltage is about 400 millivolts; and the reverse current value is measured at about 0.1 to about 1.0 seconds after the reverse test voltage is applied to the test strip.
3. The method of claim 2 , in which the working electrode comprises a plurality of microelectrodes formed from gold.
4. The method of claim 2 , in which the reagent layer comprises an enzyme, a mediator and a buffering solution in which the mediator is ruthenium hexamine chloride ranging in amount from about 15 percent to about 20 percent based on a ratio of a weight of the mediator to a volume of the buffering solution.
5. The method of claim 1 , further comprising:
wherein applying the forward test voltage comprises applying a first forward test voltage between the reference electrode and the working electrode and measuring a first forward current value near the end of the first forward test voltage, applying a second forward test voltage between the reference electrode and the working electrode and measuring a second forward current value near the end of the second forward test voltage and applying a third forward test voltage between the reference electrode and the working electrode and measuring a third forward current value near the end of the third forward test voltage;
wherein applying the reverse test voltage comprises applying a first reverse test voltage between the reference electrode and the working electrode and measuring a first reverse current value near the end of the first reverse test voltage, applying a second reverse test voltage between the reference electrode and the working electrode and measuring a second reverse current value near the end of the second reverse test voltage and applying a third reverse test voltage between the reference electrode and the working electrode and measuring a third reverse current value near the end of the third reverse test voltage;
plotting the first, second and third reverse current values as a function of an analyte concentration as measured on a reference instrument and calculating a slope m reverse of the linear regressed line obtained therefrom;
plotting the first, second and third forward current values as a function of the analyte concentration as measured on a reference instrument and calculating a slope m forward of the linear regressed line obtained therefrom;
calculating a ratio of m reverse to m forward ; and
determining if the ratio of m reverse to m forward is within an acceptance range, the acceptance range being substantially equal to two when the reference electrode is about twice the surface area of the working electrode, the first, second and third forward test voltages and first, second and third reverse test voltages are of equal magnitude and duration.
6. The method of claim 5 , in which the duration of the forward test voltage ranges from about 0.1 to about 1.0 seconds; the magnitude of the forward test voltage is about 400 millivolts;
the forward current value is measured at about 0.1 to about 1.0 seconds after the forward test voltage is applied to the test strip; the duration of the reverse test voltage ranges from about 0.1 to about 1.0 seconds; the magnitude of the reverse test voltage is about 400 millivolts; and the reverse current value is measured at about 0.1 to about 1.0 seconds after the reverse test voltage is applied to the test strip.
7. The method of claim 6 , in which the reagent layer comprises an enzyme, a mediator and a buffering solution in which the mediator is ruthenium hexamine chloride ranging in amount from about 15 percent to about 20 percent based on a ratio of a weight of the mediator to a volume of the buffering solution.