Analyte determination method and analyte meter
View Patent ↗The presence of oxygen or red blood cells in a sample applied to an electrochemical test strip that makes use of a reduced mediator is corrected for by an additive correction factor that is determined as a function of the temperature of the sample and a measurement that reflects the oxygen carrying capacity of the sample. The measured oxygen carrying capacity can also be used to determine hematocrit and to distinguish between blood samples and control solutions applied to a test strip.
1. A method for determining an analyte in a sample comprising the steps of:
(a) placing the sample in an electrochemical test cell comprising a working and a counter electrode and a mediator that serves as a charge carrier in the electrochemical determination of the analyte,
(b) electrochemically determining an uncorrected result for the determination of analyte in the sample;
(c) determining an additive correction factor for the amount of oxygen in the sample, and
(d) modifying the uncorrected result of step (b) with the correction factor of step (c) to provide a corrected determination of analyte in the sample,
wherein the additive correction factor for the amount of oxygen in the sample is determined as a function of the temperature of the sample and a measurement that reflects the oxygen carrying capacity of the sample, wherein the sample is a blood sample, the measurement that reflects the oxygen carrying capacity is hematocrit (hct) and the additive correction factor is given by the equation
additive correction factor=constant×[( S×T )+ I]×hct
wherein T is the temperature,
S and I are the slope and intercept, respectively, of a plot in which the y axis is the slope of a line plotting uncorrected analyte measurement as a function of hematocrit and the x axis is temperature, and
constant is an empirically determined constant for the particular apparatus and method of determining hematocrit.
2. The method of claim 1 , wherein hematocrit is measured by applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes, switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential.
3. The method of claim 2 , wherein the value indicative of the rate of decay is a time t mob , which is determined by determining the time, t meas , required for the potential to decay to a pre-determined voltage V mob ), and wherein t mob =t meas −t switch .
4. The method according to claim 3 , wherein the predetermined voltage is from 25 to 100 mV.
5. The method according to claim 3 , wherein the predetermined voltage is from 45 to 50 mV.
6. A meter apparatus for receiving an electrochemical test strip having 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 determining an uncorrected result for the determination of analyte in the sample, determining an additive correction factor for the amount of oxygen in the sample, and modifying the uncorrected result with the correction factor of step (c) to provide a corrected determination of analyte in the sample, wherein the additive correction factor for the amount of oxygen in the sample is determined as a function of the temperature of the sample and a measurement that reflects the oxygen carrying capacity of the sample, wherein the measurement that reflects the oxygen carrying capacity is hematocrit (hct) and the additive correction factor is given by the equation
additive correction factor=constant×[( S×T )+ I]×hct
wherein T is the temperature,
S and I are the slope and intercept, respectively, of a plot in which the y axis is the slope of a line plotting uncorrected analyte measurement as a function of hematocrit and the x axis is temperature, and
constant is an empirically determined constant for the particular apparatus and method of determining hematocrit.
7. The apparatus of claim 6 , wherein hematocrit is measured by applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes, switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential.
8. The apparatus of claim 7 , wherein the value indicative of the rate of decay is a time t mob , which is determined by determining the time, t meas , required for the potential to decay to a pre-determined voltage V mob , and wherein t mob =t meas −t switch .
9. The apparatus according to claim 8 , wherein the predetermined voltage is from 25 to 100 mV.
10. The apparatus according to claim 8 , wherein the predetermined voltage is from 45 to 50 mV.
11. The apparatus of claim 8 , wherein the apparatus fits stored data points (t,V) extending from t switch to a time after the expected time t meas to the model equation V(t)=a 1 ×ln(t)+a 2 by a least squares regression, and wherein the resulting values of a 1 and a 2 are used to calculate the value of t meas at which the potential has fallen to V mob according to the equation
t
meas
=
ⅇ
(
V
mob
-
a
1
a
2
)
.
12. The apparatus according to claim 6 , further comprising means for determining the temperature of the sample.
13. The apparatus of claim 12 , wherein hematocrit is measured by applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes, switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential.
14. The apparatus of claim 13 , wherein the value indicative of the rate of decay is a time t mob , which is determined by determining the time, t meas , required for the potential to decay to a pre-determined voltage V mob , and wherein t mob =t meas −t switch .
15. The apparatus according to claim 14 , wherein the predetermined amount is from 25 to 100 mV.
16. The apparatus according to claim 14 , wherein the predetermined amount is from 45 to 50 mV.
17. The apparatus of claim 14 , wherein the apparatus fits stored data points (t,V) extending from t switch to a time after the expected time t meas to the model equation V(t)=a 1 ×ln(t)+a 2 by a least squares regression, and wherein the resulting values of a 1 and a 2 are used to calculate the value of t meas at which the potential has fallen to V mob according to the equation
t
meas
=
ⅇ
(
V
mob
-
a
1
a
2
)
.
18. The apparatus of claim 6 , further comprising means for determining and displaying a value of hematocrit for a blood sample.
19. A measurement system comprising a meter in accordance with claim 6 , and an electrochemical test strip disposed within the housing.
20. The measurement system of claim 19 , wherein the electrochemical test strip measures glucose in a sample.
21. The measurement system of claim 20 , wherein hematocrit is measured by applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes, switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential.
22. The measurement system of claim 21 , wherein the value indicative of the rate of decay is a time t mob , which is determined by determining the time, t meas , required for the potential to decay to a pre-determined voltage V mob , and wherein t mob =t meas −t switch .
23. The measurement system of claim 22 , wherein the predetermined voltage is from 25 to 100 mV.
24. The measurement system according to claim 22 , wherein the predetermined voltage is from 45 to 50 mV.
25. The measurement system of claim 22 , wherein the measurement system fits stored data points (t,V) extending from t switch to a time after the expected time t meas to the model equation V(t)=a 1 ×ln(t)+a 2 by a least squares regression, and wherein the resulting values of a 1 and a 2 are used to calculate the value of t meas at which the potential has fallen to V mob according to the equation
t
meas
=
ⅇ
(
V
mob
-
a
1
a
2
)
.
26. The measurement system according to claim 21 , further comprising the step of comparing the value indicative of the rate of decay to a threshold value, wherein a value on one side of the threshold value indicates that the material is a blood sample, and a value on the other side of the threshold value indicates that the material is a control solution.
27. The measurement system according to claim 20 , further comprising means for determining the temperature of the sample.
28. The measurement system of claim 27 , wherein hematocrit is measured by applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes, switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential.
29. The measurement system of claim 28 , wherein the value indicative of the rate of decay is a time t mob , which is determined by determining the time, t meas , required for the potential to decay to a pre-determined voltage V mob , and wherein t mob =t meas −t switch .
30. The measurement system of claim 29 , wherein the measurement system fits stored data points (t,V) extending from t switch to a time after the expected time t meas to the model equation V(t)=a 1 ×ln(t)+a 2 by a least squares regression, and wherein the resulting values of a 1 and a 2 are used to calculate the value of t meas at which the potential has fallen to V mob according to the equation
t
meas
=
ⅇ
(
V
mob
-
a
1
a
2
)
.
31. The measurement system according to claim 28 , further comprising the step of comparing the value indicative of the rate of decay to a threshold value, wherein a value on one side of the threshold value indicates that the material is a blood sample, and a value on the other side of the threshold value indicates that the material is a control solution.
32. A method for determination of analyte in which a material is applied to an electrochemical test strip disposed in an analyte detection apparatus, wherein the material may be either a blood sample or a control solution and the signal from the test strip is processed as test sample or a calibration run based on this identification, wherein, the identification of the material as a sample or control solution is performed by the steps of:
(a) applying a potential for period for time sufficient to establish a chemical potential gradient between electrodes of the electrochemical test strip,
(b) switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential, and
(c) comparing the determined value of the rate of decay with a threshold value, wherein a value on one side of the threshold value indicates that the material is a blood sample, and a value on the other side of the threshold value indicates that the material is a control solution.
33. An apparatus for determination of analyte in which a material is applied to an electrochemical test strip disposed in an analyte detection apparatus, wherein the material may be either a blood sample or a control solution and the signal from the test strip is processed as test sample or a calibration run based on this identification, wherein, the identification of the material as a sample or control solution is performed by the steps of:
(a) means for applying a potential for period for time sufficient to establish a chemical potential gradient between electrodes of the electrochemical test strip,
(b) means for switching off the applied potential at a time t switch , and obtaining a value indicative of the rate of decay of the chemical potential gradient in the absence of applied potential, and
(c) means for comparing the determined value of the rate of decay with a threshold value, wherein a value on one side of the threshold value indicates that the material is a blood sample, and a value on the other side of the threshold value indicates that the material is a control solution.