Analyte measurement method and system with hematocrit compensation
Described and illustrated herein are systems and exemplary methods of operating an analyte measurement system having a meter and a test strip. In one embodiment, the method may be achieved by applying a first test voltage between a reference electrode and a second working electrode and applying a second test voltage between the reference electrode and a first working electrode; measuring a first test current, a second test current, a third test current and a fourth test current at the second working electrode after a blood sample containing an analyte is applied to the test strip; measuring a fifth test current at the first working electrode; estimating a hematocrit-corrected analyte concentration from the first, second, third, fourth and fifth test currents; and annunciating the hematocrit-corrected analyte concentration.
1. A method for determining a glucose concentration measurable with a system having a test strip and a meter, the method comprising:
applying a first test voltage between a reference electrode and a second working electrode coated with a reagent layer and applying a second test voltage between a reference electrode and a first working electrode coated with a reagent layer;
measuring a first test current, a second test current, a third test current and a fourth test current at the second working electrode in which blood containing glucose is applied to the test strip to cause a transformation of the glucose in the blood from one form of glucose into another form of glucose and generate a current by an electrochemical re-oxidation of a reduced mediator applied to the test strip;
measuring a fifth test current at the first working electrode;
determining the glucose concentration from the first, second, third, fourth and fifth test currents with an equation of the form:
G
=
(
a
*
I
5
+
b
(
c
*
(
I
2
-
I
1
d
)
+
e
f
*
(
I
2
*
I
1
)
+
g
)
*
(
h
*
(
I
4
-
I
3
k
)
+
p
q
*
(
I
4
*
I
3
)
+
s
)
)
-
intercept
slope
where:
G comprises the glucose concentration;
I 1 comprises the first test current;
I 2 comprises the second test current;
I 3 comprises the third test current;
I 4 comprises the fourth test current;
I 5 comprises the fifth test current;
a, b, c, d, e, f, g, h, k, p, q and s each comprises empirically derived constants;
intercept comprises an intercept value determined from a linear regression of a plot of
a
*
I
5
+
b
(
c
*
(
I
2
-
I
1
d
)
+
e
f
*
(
I
2
*
I
1
)
+
g
)
*
(
h
*
(
I
4
-
I
3
k
)
+
p
q
*
(
I
4
*
I
3
)
+
s
)
versus a reference glucose concentration; and
slope comprises a slope value determined from a linear regression of a plot of
a
*
I
5
+
b
(
c
*
(
I
2
-
I
1
d
)
+
e
f
*
(
I
2
*
I
1
)
+
g
)
*
(
h
*
(
I
4
-
I
3
k
)
+
p
q
*
(
I
4
*
I
3
)
+
s
)
versus the reference glucose concentration.
2. The method of claim 1 , in which the reference electrode, the first electrode and the second electrodes are disposed on a single plane.
3. The method of claim 1 , in which the first test current is measured from about 2.18 to about 2.26 seconds after initiation of the measuring.
4. The method of claim 1 , in which the second current is measured from about 2.90 to about 2.98 seconds after initiation of the measuring.
5. The method of claim 1 , in which the third current is measured from about 3.01 to about 3.09 seconds after initiation of the measuring.
6. The method of claim 1 , in which the fourth current is measured from about 0.95 to about 1.03 seconds after initiation of the measuring.
7. The method of claim 1 , in which the fifth current is measured from about 4.74 to about 4.82 seconds after initiation of the measuring.
8. The method of claim 1 , in which a comprises from about 0.0158 to about 0.0162, b comprises from about 3.55 to about 3.59, c comprises from about 24.2 to about 24.6, d comprises from about 71.1 to about 71.5, e comprises from about 6.89 to about 6.93, f comprises from about 0.27 to about 0.31, g comprises from about 81.8 to about 82.2, h comprises from about 102 to about 104, k comprises from about −453 to about −455, p comprises from about −0.0686 to about −0.0690 and q comprises from about 30.2 to about 30.6.
9. The method of claim 1 , in which the slope comprises a value of about minus 0.000545 and the intercept comprises a value of about minus 2.86.
10. A method for determining a hematocrit-corrected test current measurable with a system having a test strip and a meter, the method comprising:
applying a first test voltage between a reference electrode and a second working electrode coated with a reagent layer and applying a second test voltage between a reference electrode and a first working electrode coated with a reagent layer;
measuring a first test current, a second test current, a third test current and a fourth test current at the second working electrode in which blood containing glucose is applied to the test strip to cause a transformation of the glucose in the blood from one form of glucose into another form of glucose and generate a current by an electrochemical re-oxidation of a reduced mediator applied to the test strip;
measuring a fifth test current at the first working electrode; and
determining the hematocrit-corrected test current by determining a ratio of a third corrected current to a first corrected current multiplied by a second corrected current.
11. The method of claim 10 , in which the third corrected current comprises a value determined by an equation of the form:
ic 3= a*I 5 +b
where:
ic3 comprises the third corrected current;
I 5 comprises the fifth test current; and
a and b each comprises an empirically derived constant.
12. The method of claim 10 , in which the first corrected current comprises a value determined by an equation of the form:
ic
1
=
c
*
(
I
2
-
I
1
d
)
+
e
f
*
(
I
2
*
I
1
)
+
g
where:
ic1 comprises the third corrected current;
I 1 comprises the first test current;
I 2 comprises the second test current; and
c, d, e, f and g comprise empirically derived constants.
13. The method of claim 10 , in which the second corrected current comprises a value determined by an equation of the form:
ic
2
=
h
*
(
I
4
-
I
3
k
)
+
p
q
*
(
I
4
*
I
3
)
+
s
where:
ic2 comprises the third corrected current;
I 3 comprises the third test current;
I 4 comprises the fourth test current; and
h, k, p, q and s comprise empirically derived constants.
14. The method of claim 10 , in which the first test current comprises a current measured from about 2.18 to about 2.26 seconds after initiation of the measuring; the second current comprises a current measured from about 2.90 to about 2.98 seconds after initiation of the measuring; the third current comprises a current measured from about 3.01 to about 3.09 seconds after initiation of the measuring; the fourth current comprises a current measured from about 0.95 to about 1.03 seconds after initiation of the measuring; and the fifth current comprises a current measured from about 4.74 to about 4.82 seconds after initiation of the measuring.