Hematocrit corrected glucose measurements for electrochemical test strip using time differential of the signals
Various embodiments that allow for determination of hematocrit by a time differential between the input and output signals such that a glucose measurement for a blood sample can be corrected by the measured hematocrit of the blood sample.
1. A method to determine a glucose concentration in a blood sample, the method comprising:
depositing a blood sample in a test chamber of a test strip having at least first and second electrodes in contact with a reagent and third and fourth electrodes not in contact with the reagent;
driving a non-oscillating signal to the at least first and second electrodes to cause a reaction with the glucose in the blood sample and the reagent;
measuring a current output of the reaction to establish a preliminary glucose concentration;
applying a first oscillating input signal at a first frequency to third and fourth electrodes;
detecting a first oscillating output signal from the third and fourth electrodes;
measuring a first time differential between the first input and output oscillating signals;
applying a second oscillating input signal at a second frequency to the third and fourth electrodes;
detecting a second oscillating output signal from the third and fourth electrodes;
measuring a second time differential between the first input and output oscillating signals;
estimating a hematocrit of the blood sample based on the first and second time differentials; and
deriving a final glucose concentration based on the preliminary glucose concentration and the hematocrit from the estimating step.
2. The method of claim 1 , in which the first frequency comprises about 25,000 Hertz and the second frequency comprises about 250,000 Hertz.
3. The method of claim 2 , in which the estimating comprises applying an equation of the form
HCT
EST
=
(
C
1
Δ
t
1
-
C
2
Δ
t
2
-
C
3
)
m
1
Where each of C 1 , C 2 , and C 3 comprises an operational constant for the test strip.
4. The method of claim 3 , in which the measuring of a current output for the preliminary glucose concentration is performed prior to the estimating of the hematocrit.
5. The method of claim 3 , in which the deriving comprises calculating the final glucose concentration G F from:
G
F
=
(
I
E
1
-
k
(
HCT
EST
-
h
0
)
)
-
c
3
m
3
where
I E comprises a magnitude of the measured end current
HCT EST comprises the hematocrit,
h 0 comprises nominal hematocrit,
and k, m 3 and c 3 comprise parameters from regression data.