System and method for measuring an analyte in a sample
Methods of determining a corrected analyte concentration in view of some error source are provided herein. The methods can be utilized for the determination of various analytes and/or various sources of error. In one example, the method can be configured to determine a corrected glucose concentration in view of an extreme level of hematocrit found within the sample. In other embodiments, methods are provided for identifying various system errors and/or defects. For example, such errors can include partial-fill or double-fill situations, high track resistance, and/or sample leakage. Systems are also provided for determining a corrected analyte concentration and/or detecting some system error.
1. A method of identifying a defect in a test strip, comprising:
applying a first test voltage V 1 for a first test time interval T 1 between a first electrode and a second electrode sufficient to oxidize a reduced mediator at the second electrode;
applying a second test voltage V 2 for a second test time interval T 2 between a first electrode and a second electrode sufficient to oxidize a reduced mediator at the first electrode and in which the polarity of the first test voltage V 1 is opposite the polarity of the second test voltage V 2 ;
measuring a first test current i 1 and a second test current i 2 that occur during the second test time interval T 2 , the second test current i 2 occurring after the first test current i 1 ; and
determining whether the test strip has the defect using an equation based on the first test current i 1 and the second test current i 2 .
2. The method of claim 1 , wherein the second test voltage V 2 is applied immediately after the first test voltage V 1 .
3. The method of claim 1 , wherein the equation comprises a ratio between the first test current i 1 and the second test current i 2 .
4. The method of claim 3 , wherein the equation comprises a ratio between the first test current i 1 and the difference between the first test current i 1 and the second test current i 2 .
5. The method of claim 1 , wherein the first test current i 1 is determined at about a beginning of the second time interval T 2 .
6. The method of claim 1 , wherein the first test current i 1 is a maximum current value occurring during the second time interval T 2 .
7. The method of claim 1 , wherein the second test current i 2 is determined at about an end of the second time interval T 2 .
8. The method of claim 1 , wherein the second test current i 2 is a minimum current value occurring during the second time interval T 2 .
9. The method of claim 8 , further comprising a step of providing an error message indicating a defective test strip if the ratio is greater than a first predetermined threshold.
10. The method of claim 9 , wherein the first predetermined threshold is about 1.2.
11. The method of claim 1 , wherein the equation is a
ratio
=
i
1
i
1
-
i
2
,
where i 1 is the first test current and i 2 is the second test current.
12. The method of claim 1 , wherein the first test voltage ranges from about zero to about −600 mV with respect to the second electrode.
13. The method of claim 1 , wherein the second test voltage ranges from about 10 mV to about 600 mV with respect to the second electrode.
14. The method of claim 1 , wherein the defect is a high track resistance R.
15. The method of claim 14 , wherein the high track resistance R is between a connection point on a meter and either the first or second electrode of the test strip.
16. The method of claim 1 , in which each of V 1 and V 2 are DC voltages.
17. A method of identifying a defect in a test strip comprising:
applying a first test voltage V 1 for a first test time interval T 1 between a first electrode and a second electrode sufficient to oxidize a reduced mediator at the second electrode;
applying a second test voltage V 2 for a second test time interval between a first electrode and a second electrode sufficient to oxidize a reduced mediator at the first electrode;
measuring a first test current i 1 , a second test current i 2 , a third test current i 3 , and a fourth test current i 4 that occur during the second test time interval T 2 ;
calculating a first logarithm of a first ratio based on the first test current i 1 and the second test current i 2 ;
calculating a second logarithm of a second ratio based on the third test current i 3 and the fourth test current i 4 ; and
determining whether the test strip has a defect using an equation based on the first logarithm and the second logarithm.
18. The method of claim 17 , wherein the defect is a leakage of fluid between a spacer and the first electrode.
19. The method of claim 17 , wherein a reagent layer is disposed on the first electrode so that a portion of the reagent layer is between the spacer and the first electrode.
20. The method of claim 17 , wherein the equation is a third ratio represented by
log
(
i
1
i
2
)
log
(
i
3
i
4
)
,
where i 1 is the first test current, i 2 is the second test current, i 3 is the third test current, and i 4 is the fourth test current.
21. The method of claim 17 , further comprising a step of providing an error message indicating a defective test strip if the third ratio is less than a predetermined threshold.
22. The method of claim 17 , wherein the predetermined threshold is about 1.
23. The method of claim 21 , wherein the predetermined threshold is about 0.95.
24. The method of claim 17 , wherein the first test current i 1 and the second test current i 2 comprise the two largest current values during the second time interval T 2 .
25. The method of claim 17 , wherein the fourth test current i 4 is a smallest current value occurring the second time interval T 2 .
26. The method of claim 17 , wherein a difference between a fourth test current time and a third test current time is greater than a difference between a second test current time and a first test current time.
27. A method of identifying an error in performing a test with a test strip, comprising:
applying a first test voltage V 1 for a first test time interval T 1 between a first electrode and a second electrode;
measuring consecutively a first test current i 1 , a second test current i 2 , and a third test current i 3 ; and
determining whether an error was performed by using an equation based on the second test current i 2 and a summation of the absolute value of the first test current i 1 and the absolute value of the third test current i 3 .
28. The method of claim 27 , wherein a time difference between the measurements of the first test current i 1 and the second test current i 2 ranges from about one nanosecond to about 100 milliseconds.
29. The method of claim 27 , wherein a time difference between the measurements of the first test current i 1 and the third test current i 3 ranges from about one nanosecond to about 100 milliseconds.
30. The method of claim 27 , wherein the equation is Y=2*abs(i(t))−abs(i(t−x))−abs(i(t+x)), where i(t) is the second test current, i(t−x) is the first test current, i(t+x) is the third test current, t is a time, and x is an increment of time, and abs represents an absolute function.
31. The method of claim 27 , wherein the equation is Z=abs(i(t+x))−abs(i(t)), where i(t) is the second test current, i(t+x) is the third test current, t is a time, and x is an increment of time, and abs represents an absolute function.