System and method for measuring an analyte in a sample and correcting for interferents
Methods and systems to apply a plurality of test voltages to the test strip and measure a current transient output resulting from an electrochemical reaction in a test chamber of the test strip so that a glucose concentration can be determined that account for interferent substances in the body fluid sample. A method of determining blood glucose concentration with a glucose measurement system that includes a test strip and test meter. The test meter has a microcontroller configured to apply a plurality of test voltages to the test strip and measure a current transient output resulting from an electrochemical reaction in a test chamber of the test strip.
1. A method of determining blood glucose concentration with a glucose measurement system that includes a test strip and test meter, the test meter having a microcontroller configured to apply a plurality of test voltages comprising first, second and third test voltages to the test strip and measure a current transient output resulting from an electrochemical reaction in a test chamber of the test strip, the method comprising:
inserting the test strip into a strip port connector of the test meter to connect at least two electrodes of the test strip to a strip measurement circuit;
initiating a test sequence after deposition of a sample by causing the first test voltage to be applied, the first test voltage causing a transformation of analytes in the sample from one form to a different form;
switching a first test voltage to a second test voltage different than the first test voltage;
changing the second test voltage to a third test voltage different from the second voltage;
measuring a second current output of the current transient from the electrodes after the changing from the second test voltage to the third test voltage;
estimating a current that approximates a steady state current output of the current transient after the third test voltage is maintained at the electrodes;
calculating a blood glucose concentration based on the first, second and third current output of the current transient with an equation of the form:
G
1
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where: G 1 comprises a glucose concentration;
i
r
=
∑
t
=
4.4
t
=
5
i
(
t
)
;
i
l
=
∑
t
=
1.4
t
=
4
i
(
t
)
;
i
2
(
Corr
)
=
(
i
4.1
+
b
i
5
-
c
i
1.1
i
4.1
+
b
i
5
)
i
r
where:
a, b, c, p, zgr comprise manufacturing parameters;
i 4.1 comprises the current measured at about 4.1 seconds after initiation of test sequence;
i 5 comprises the current measured at about 5 seconds after initiation of test sequence;
i 1.1 comprises the current measured at about 1.1 seconds after initiation of test sequence; and
correcting the blood glucose concentration with an equation of the form:
G corr =G 1 *( A+B*i 1.1 )
where G corr comprises a corrected blood glucose concentration and coefficients A and B comprise empirically derived coefficients.
2. The method of claim 1 , in which the coefficients A and B comprise approximately 1.004 and approximately 0.0077, respectively.
3. A method of determining blood glucose concentration with a glucose measurement system that includes a test strip and test meter, the test meter having a microcontroller configured to apply a plurality of test voltages comprising a first test voltage, a second test voltage, and a third test voltage to the test strip and measure a current transient output resulting from an electrochemical reaction in a test chamber of the test strip, the method comprising:
inserting the test strip into a strip port connector of the test meter to connect at least two electrodes of the test strip to a strip measurement circuit;
initiating a test sequence after deposition of a sample by applying the first test voltage;
causing a transformation of analytes in the sample from one form to a different form;
switching the first test voltage to a second test voltage different than the first test voltage;
changing the second test voltage to a third test voltage different from the second voltage;
measuring a second current output of the current transient from the electrodes after the changing from the second test voltage to the third test voltage;
estimating approximate steady state current output of the current transient after the third test voltage is maintained at the electrodes;
calculating a blood glucose concentration based on the first, second and third current output of the current transient with an equation of the form:
G
1
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where: G 1 comprises a glucose concentration;
i
r
=
∑
t
=
4.4
t
=
5
i
(
t
)
;
i
l
=
∑
t
=
1.4
t
=
4
i
(
t
)
;
i
2
(
Corr
)
=
(
i
4.1
+
b
i
5
-
c
i
1.1
i
4.1
+
b
i
5
)
i
r
where:
a, b, c, p, zgr comprise manufacturing parameters;
i 4.1 comprises the current measured at about 4.1 seconds after initiation of test sequence;
i 5 comprises the current measured at about 5 seconds after initiation of test sequence;
i 1.1 comprises the current measured at about 1.1 seconds after initiation of test sequence; and
correcting the blood glucose concentration with an equation of the form:
G corr =G 1 *( C+D*i 1.1 +E *( i 1.1 ) 2 )
where G corr comprises a corrected blood glucose concentration and coefficients C, D and E comprise empirically derived coefficients.
4. The method of claim 3 , in which the step of switching comprises changing the polarity of the second test voltage with respect to the first test voltage.
5. The method of claim 3 , in which the deriving of the first corrected glucose concentration comprises calculating with equations of the form:
G
1
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where: G 1 comprises a glucose concentration;
i
r
=
∑
t
=
4.4
t
=
5
i
(
t
)
;
i
l
=
∑
t
=
1.4
t
=
4
i
(
t
)
;
i
2
(
Corr
)
=
(
i
4.1
+
b
i
5
-
c
i
1.1
i
4.1
+
b
i
5
)
i
r
where:
a, b, c, p, zgr comprise manufacturing parameters;
i 4.1 comprises the current measured at about 4.1 seconds after initiation of test sequence;
i 5 comprises the current measured at about 5 seconds after initiation of test sequence;
i 1.1 comprises the current measured at about 1.1 seconds after initiation of test sequence; and
G corr1 =G 1 *( A+B*i 1.1 )
where G corr1 comprises a first corrected blood glucose concentration and coefficients A and B comprise empirically derived coefficients.
6. The method of claim 3 , in which the deriving of the second corrected glucose concentration comprises calculating with equations of the form
G
1
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where: G 1 comprises a glucose concentration;
i
r
=
∑
t
=
4.4
t
=
5
i
(
t
)
;
i
l
=
∑
t
=
1.4
t
=
4
i
(
t
)
;
i
2
(
Corr
)
=
(
i
4.1
+
b
i
5
-
c
i
1.1
i
4.1
+
b
i
5
)
i
r
where:
a, b, c, p, zgr comprise manufacturing parameters;
i 4.1 comprises the current measured at about 4.1 seconds after initiation of test sequence;
i 5 comprises the current measured at about 5 seconds after initiation of test sequence;
i 1.1 comprises the current measured at about 1.1 seconds after initiation of test sequence; and
correcting the blood glucose concentration with an equation of the form:
G corr2 =G 1 *( C+D*i 1.1 +E *( i 1.1 ) 2 )
where G corr2 comprises a corrected blood glucose concentration and coefficients C, D and E comprise empirically derived coefficients.
7. The method of claim 3 , in which the measuring of the first current output comprises measuring a current output of the at least two electrodes at about 1.1 seconds after initiation of test sequence.
8. The method of claim 3 , in which the measuring of the second current output comprises measuring a current output of the at least two electrodes at about 4.1 seconds after initiation of test sequence.
9. The method of claim 3 , in which the estimating of the steady state current output comprises measuring a current output of the at least two electrodes at about 5 seconds after initiation of test sequence.
10. The method of claim 3 , in which the coefficients A, B, C, D, and E comprise approximately 1.004, approximately 0.0077, approximately 0.889, approximately 0.0220 and approximately −0.00036, respectively.
11. The method of claim 5 , in which the coefficients A and B comprise approximately 1.004 and approximately 0.0077, respectively.
12. The method of claim 5 , in which the coefficients C, D, and E comprise approximately 0.889, approximately 0.0220 and approximately −0.00036, respectively.
13. The method of claim 5 , in which the manufacturing parameter a comprises approximately 0.192, b comprises approximately 0.68, c comprises approximately 2, p comprises approximately 0.52, and zgr comprises approximately 2.
14. The method of claim 3 , in which the threshold percentage is greater than 10% difference in glucose concentrations.
15. A blood glucose measurement system comprising:
an analyte test strip including:
a substrate having a reagent disposed thereon;
at least two electrodes proximate the reagent in test chamber;
an analyte meter including:
a strip port connector disposed to connect to the two electrodes;
a power supply; and
a microcontroller electrically coupled to the strip port connector and the power supply, the microcontroller programmed to,
apply a first test voltage;
switch the first test voltage to a second test voltage different than the first test voltage;
change the second test voltage to a third test voltage different from the second test voltage,
measure a second current output of the current transient from the electrodes after the change from the second test voltage to the third test voltage,
estimate a current that approximates a steady state current output of the current transient after the third test voltage is maintained at the electrodes, and
determine a glucose concentration G 1 and a corrected glucose concentration G corr to account for interfering agents so that at least 97% of corrected test results are within respective bias criterion of ±10 mg/dL at 65 mg/dL, 240 mg/dL, or at 450 mg/dL as compared to reference YSI data; ±12 mg/dL at 65 mg/dL, 240 mg/dL, or 450 mg/dL as compared to reference YSI data; and ±15 mg/dL at 65 mg/dL, 240 mg/dL, or 450 mg/dL as compared to reference YSI data, the glucose concentration and the corrected glucose concentration based on the first, second and third current output and being derived from the following equations:
G
1
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where: G 1 comprises a glucose concentration;
i
r
=
∑
t
=
4.4
t
=
5
i
(
t
)
;
i
l
=
∑
t
=
1.4
t
=
4
i
(
t
)
;
i
2
(
Corr
)
=
(
i
4.1
+
b
i
5
-
c
i
1.1
i
4.1
+
b
i
5
)
i
r
where:
a, b, c, p, zgr comprise manufacturing parameters;
i 4.1 comprises the current measured at about 4.1 seconds after initiation of test sequence;
i 5 comprises the current measured at about 5 seconds after initiation of test sequence;
i 1.1 comprises the current measured at about 1.1 seconds after initiation of test sequence; and
G corr =G 1 *( C+D*i 1.1 +E *( i 1.1 ) 2 )
where G corr comprises a corrected blood glucose concentration and coefficients C, D and E comprise empirically derived coefficients.
16. The system of claim 15 , in which the manufacturing parameters a, b, c, p, zgr are such that a comprises approximately 0.192, b comprises approximately 0.68, c comprises approximately 2, p comprises approximately 0.52 and zgr comprises approximately 2.
17. The system of claim 15 , in which the coefficients C, D, and E comprise approximately 0.889, approximately 0.0220 and approximately −0.00036, respectively.