System and method for measuring an analyte in a sample and calculating glucose results to account for physical characteristics of the sample
View Patent ↗Described are 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 hematocrits in both typical subjects and neonates.
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 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;
determining at least one physical characteristic of the sample, the at least one physical characteristic being one of a hematocrit level, a viscosity, or a density of the sample;
transforming analytes in the sample from one form to a different form;
switching a first voltage to a second voltage different than the first voltage, the switching comprises changing the polarity of the second voltage with respect to the first voltage;
measuring a first current output of the current transient from the at least two electrodes of the test strip after the changing from the first voltage to the second voltage;
changing the second voltage to a third voltage different from the second voltage;
measuring a second current output of the current transient from the at least two electrodes of the test strip after the changing from the second voltage to the third voltage;
estimating a current that approximates a steady state current output of the current transient after the third voltage is maintained at the at least two electrodes of the test strip, the estimated current being a third current output of the current transient;
obtaining analyte calculation coefficients of the test chamber based on the at least one physical characteristic of the sample; and
calculating the blood glucose concentration based on the first, second and third current outputs of the current transient and the analyte calculation coefficients.
2. The method of claim 1 , in which the blood glucose concentration is obtained with an equation of the form:
G
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where
:
G
comprises
the
blood
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, p, and zgr are determined from the obtaining step;
b comprises approximately 0.205;
c comprises approximately 2;
i 4.1 comprises the first current output measured at approximately 4.1 seconds after initiation of test sequence;
i 5 comprises the third current output measured at approximately 5 seconds after initiation of test sequence; and
i 1.1 comprises the first current output measured at approximately 1.1 seconds after initiation of test sequence.
3. The method of claim 1 , in which the determining of the at least one physical characteristic of the sample comprises:
driving an alternating signal into the test chamber;
measuring an impedance from an output signal of the test chamber; and
correlating the impedance with the hematocrit level of the sample.
4. The method of claim 1 , in which the determining of the at least one physical characteristic of the sample comprises:
determining an age of the subject from birth to no more than one year old; and
selecting the hematocrit level based on the age.
5. The method of one of claim 3 or claim 4 , in which the obtaining comprises selecting from a look-up table having the analyte calculation coefficients for each level of hematocrit.
6. A method of determining blood glucose concentration with a glucose measurement system that includes a biosensor and test meter, the test meter having a microcontroller configured to apply a plurality of test voltages to at least two electrodes of the biosensor and measure a current transient output resulting from an electrochemical reaction in a test chamber of the biosensor, the method comprising:
initiating a test sequence after deposition of a sample;
transforming analytes in the sample from one form to a different form;
switching a first voltage to a second voltage different than the first voltage, the switching comprises changing the polarity of the second voltage with respect to the first voltage;
measuring a first current output of the current transient from the at least two electrodes after the changing from the first voltage to the second voltage;
changing the second voltage to a third voltage different from the second voltage;
measuring a second current output of the current transient from the at least two electrodes after the changing from the second voltage to the third voltage;
estimating an approximate steady state current output of the current transient after the third voltage is maintained at the at least two electrodes, the estimated approximated steady state current output being a third current output of the current transient;
calculating a blood glucose concentration based on the first, second and third current outputs of the current transient with an equation of the form:
G
=
(
i
r
i
l
)
p
(
a
i
2
CORR
-
zgr
)
;
where
:
G
comprises
the
blood
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 comprises approximately 0.171;
b comprises approximately 0.678;
c comprises approximately 2;
p comprises approximately 0.433;
zgr comprises approximately 4;
i 4.1 comprises the second current output measured at approximately 4.1 seconds after initiation of test sequence;
i 5 comprises the third current output measured at approximately 5 seconds after initiation of test sequence; and
i 1.1 comprises the first current output measured at approximately 1.1 seconds after initiation of test sequence.
7. The method of claim 6 , in which coefficients p, a, and zgr for samples with approximately 20% hematocrit comprise respectively, 0.35, 0.6459 and 1.95, the coefficients p, a, and zgr for samples with approximately 30% hematocrit comprise respectively 0.2703, 0.6915, and 1.9522, the coefficients p, a, and zgr for samples with approximately 40% hematocrit comprise respectively 0.2148, 0.7572, and 1.96; the coefficients p, a, and zgr for samples with approximately50% hematocrit comprise respectively 0.1055, 0.9134 and 0.196; the coefficients p, a, and zgr for samples with approximately 60% hematocrit comprise respectively 0.087, 1.0655, and 2.02, the coefficients p, a, and zgr for samples with approximately 70% hematocrit comprise respectively 0.0058, 1.4586, and 1.97, the coefficients p, a, and zgr for samples with approximately 80% hematocrit comprise respectively −0.0809, 2.2413 and 2.2413.
8. The method of claim 6 , in which coefficients p, a, and zgr for samples with hematocrits in a range of 30-40% hematocrit comprise respectively 0.3156, 0.6686 and 1.5757; the coefficients p, a, and zgr for samples with hematocrits in a range of 50-60% hematocrit comprise respectively 0.2592, 0.7509 and 0.5530; the coefficients p, a, and zgr for samples with hematocrits in a range of 70-80% hematocrit comprise respectively 0.0768, 1.3463 and −1.2513.