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 hematocrit of a blood sample comprising the steps of:
(a) introducing a blood sample between first and second electrodes in an electrochemical test cell containing a redox active species that serves as a charge carrier;
(b) applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes,
(c) 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
(d) comparing the determined value of the rate of decay with a standard curve relating rate of decay to hematocrit to arrive at a value for the hematocrit of the sample.
2. The method of claim 1 , wherein the value indicative of the rate of decay of the chemical potential gradient 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 t mob , and wherein t mob =t meas −t switch .
3. An apparatus for measurement of hematocrit 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 for period for time sufficient to establish a chemical potential gradient in a blood sample received 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, and
(d) means for comparing the determined value of the rate of decay with a standard curve relating rate of decay to hematocrit to arrive at a value for the hematocrit of the sample.
4. The apparatus of claim 3 , wherein the value indicative of the rate of decay of the chemical potential gradient 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 .
5. The apparatus of claim 4 , 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 X 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
)
.
6. A method for determining an indication of anemia using a blood sample comprising the steps of:
(a) introducing a blood sample between first and second electrodes in an electrochemical test cell containing a redox active species that serves as a charge carrier;
(b) applying a potential for period for time sufficient to establish a chemical potential gradient between the electrodes,
(c) 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
(d) comparing the determined value of the rate of decay with a standard value for the rate of decay corresponding to a threshold value indicative of anemia.
7. The method of claim 6 , wherein the value indicative of the rate of decay of the chemical potential gradient 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 .
8. An apparatus for assessment of anemia comprising:
(a) a housing having a slot for receiving an electrochemical test strip;
(b) communications means for receiving input from and communicating an assessment of anemia to a user; and
(c) means for applying a potential for period for time sufficient to establish a chemical potential gradient in a blood sample received 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, and
(d) means for comparing the determined value of the rate of decay with a standard value a standard value for the rate of decay corresponding to a threshold value indicative of anemia.
9. The apparatus of claim 8 , wherein the value indicative of the rate of decay of the chemical potential gradient 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 .
10. The apparatus of claim 3 , wherein the predetermined amount is from 25 to 100 mV.
11. The apparatus of claim 3 , wherein the predetermined amount is from 45 to 50 mV.
12. The apparatus of claim 3 , further comprising means for measuring the temperature in the test cell.
13. The method of claim 1 , wherein the predetermined amount is from 25 to 100 mV.
14. The method of claim 1 , wherein the predetermined amount is from 45 to 50 mV.
15. The method of claim 1 , further comprising the step of measuring the temperature in the test cell, wherein the standard curve relating rate of decay to hematocrit that is used to arrive at a value for the hematocrit of the sample is selected based on the measured temperature.