Systems, devices, and methods for measuring whole blood hematocrit based on initial fill velocity
Methods for determining the hematocrit of a blood sample, and devices and systems used in conjunction with the same. The hematocrit value can be determined on its own, and further, it can be further used to determine a concentration of an analyte in a sample. In one exemplary embodiment of a method for determining the hematocrit value in a blood sample, a volume of blood is provided in a sample analyzing device having a working and a counter electrode. An electric potential is applied between the electrodes and an initial fill velocity of the sample into the device is calculated. The hematocrit of the blood, as well as a concentration of an analyte in view of the initial fill velocity can then be determined. Systems and devices that take advantage of the use of an initial fill velocity to determine hematocrit levels and make analyte concentration determinations are also provided.
1. A method for determining an analyte of a whole blood sample, the method comprising the steps of:
providing a sample of whole blood to a sample analyzing device having a capillary space;
measuring an initial fill velocity of the sample in at least a portion of the capillary space in which the initial velocity is measured by:
applying an electrical potential;
measuring an electrical current; and
determining an initial current flow;
determining a hematocrit value of the blood sample solely from the measured initial fill velocity using an equation that requires the determined initial current flow and wherein the sample includes an analyte, and
calculating a concentration of the analyte by:
applying an electric potential;
measuring an initial current after applying the electric potential;
reversing the electric potential;
measuring a change in current over time following the reversal of the electric potential as a slope (m) of a current versus time graph; and
using an equation that requires the determined hematocrit value and the measured change in current over time.
2. The method of claim 1 , wherein the step of measuring an initial fill velocity further comprises the additional steps of:
performing current measurements approximately every 10 milliseconds for at least approximately 50 milliseconds; and
calculating an average current based on the current measurements.
3. The method of claim 1 , wherein the step of measuring an initial fill velocity of the sample occurs after the sample enters the capillary space.
4. The method of claim 1 , wherein the step of measuring an initial fill velocity of the sample occurs after the sample crosses into a region of the capillary space of the sample analyzing device where a detection signal is generated.
5. The method of claim 1 , further comprising the step of at least one of measuring a temperature of the sample and inferring a temperature of the sample.
6. The method of claim 1 , wherein the sample analyzing device is an immunosensor.
7. The method of claim 1 , further comprising the step of at least one of measuring a temperature of the sample and inferring the temperature of the sample.
8. The method of claim 7 , further comprising the step of measuring a change in current over a period of time after the step of reversing the electric potential, wherein the step of calculating a concentration of the analyte comprises the additional step of calculating the concentration of the analyte in view of the change in current over the period of time and the temperature of the sample.
9. The method of claim 1 , wherein the equation for determining the hematocrit value is
H= 97.6−1.7658| i i |
in which |i i | is the absolute value of the initial current.
10. The method of claim 5 , including the equation for determining the hematocrit value is
H= 77.1−2.1| i i |+0.75T
in which |i i | is the absolute value of the initial current and T is the temperature of the sample.
11. The method of claim 1 , in which the equation for determining analyte concentration is C O =−3.5+0.866 exp(y)
in which C O is the concentration of analyte and
y
=
m
(
1
-
0.01
H
)
0.83
in which m is the slope of the current versus time curve, and H is the determined hematocrit value.
12. The method of claim 8 , in which the equation for determining analyte concentration is C O =−5.7+1.78 exp(y′)
in which C O is the concentration of the analyte and
y
′
=
y
1
+
0.068
(
T
-
25
)
,
in which T is the temperature of the sample and
y
=
m
(
1
-
0.01
H
)
1.55
and
m is the slope of a current versus time curve and H is the determined hematocrit value.