Dual Frequency Impedance Measurement of Hematocrit in Strips
This invention is a method for determining a hematocrit value. The steps include applying a first pulse of potential excitation at a first frequency to a test strip containing a fluid sample. The method also includes applying a second pulse at a second frequency that is higher than the first frequency. Based on first and second impedance measurements associated with each pulse, a hematocrit value may be determined. Also, a concentration of an analyte contained within the fluid sample may be determined based on the hematocrit value.
1 . A method for determining a hematocrit value of a sample fluid, comprising:
providing a sample fluid to a test strip;
applying to the test strip a first pulse at a first frequency and a second pulse at a second frequency, wherein the second frequency is at least about 20 kHz and higher than the first frequency;
measuring a first impedance associated with the first pulse and a second impedance associated with the second pulse; and
determining a hematocrit value based on the first and second impedance measurements.
2 . The method of claim 1 , wherein the first frequency is greater than at least one of 10 kHz, 50 kHz, 100 kHz, and 1 MHz.
3 . The method of claim 1 , wherein the second frequency is higher than the first frequency by a multiple of at least one of 2, 5, 10, 20, 50, and 100.
4 . The method of claim 1 , wherein impedance includes at least one of a resistive component, a reactive component, and a phase angle.
5 . The method of claim 1 , further comprising:
determining a concentration of an analyte within the sample fluid based in part on the hematocrit value.
6 . The method of claim 5 , wherein the analyte is glucose.
7 . The method of claim 6 , wherein the sample fluid includes an enzyme of at least one of glucose oxidase and glucose dehydrogenase and a mediator of at least one of potassium ferricyanide and hexaammineruthenium chloride.
8 . The method of claim 1 , further comprising:
determining a calibration curve based on one or more hematocrit values.
9 . The method of claim 1 , wherein the first pulse is applied following the application of the second pulse.
10 . A system for determining a hematocrit value of a sample fluid, comprising:
a set of electrodes configured to apply an excitation pulse to the sample fluid;
a processor configured to:
measure a first impedance associated with a first pulse, wherein the first pulse is applied to a sample fluid and the first pulse has a first frequency;
measure a second impedance associated with a second pulse, wherein the second pulse is applied to the sample fluid, and has a second frequency that is at least about 20 kHz and higher than the first frequency; and
determine a hematocrit value based on the first and second impedance measurements.
11 . The system of claim 10 , wherein the first frequency is greater than at least one of 10 kHz, 50 kHz, 100 kHz, and 1 MHz.
12 . The system of claim 10 , wherein the second frequency is higher than the first frequency by a multiple of at least one of 2, 5, 10, 20, 50, and 100.
13 . The system of claim 10 , wherein impedance includes at least one of a resistive component, a reactive component, and a phase angle.
14 . The system of claim 10 , wherein the processor is further configured to determine a concentration of an analyte within the sample fluid based in part on the hematocrit value.
15 . The system of claim 14 , wherein the analyte is glucose.
16 . The system of claim 15 , wherein the sample fluid includes an enzyme of at least one of glucose oxidase and glucose dehydrogenase and a mediator of at least one of potassium ferricyanide and hexaammineruthenium chloride.
17 . The system of claim 10 , wherein the processor is further configured to determine a calibration curve based on one or more hematocrit values.
18 . The system of claim 10 , further including a display configured to show the hematocrit value.
19 . The system of claim 10 , wherein the processor is further configured to apply the first pulse following application of the second pulse.
20 . A computer readable media, wherein the media comprises a plurality of instructions configured to direct a processor to:
measure a first impedance associated with a first pulse, wherein the first pulse is applied to a sample fluid and the first pulse has a first frequency;
measure a second impedance associated with a second pulse, wherein the second pulse is applied to the sample fluid, and has a second frequency that is at least about 20 kHz and higher than the first frequency; and
determine a hematocrit value based on the first and second impedance measurements.
21 . The computer readable media of claim 20 , wherein the first frequency is greater than at least one of 10 kHz, 50 kHz, 100 kHz, and 1 MHz.
22 . The computer readable media of claim 20 , wherein the second frequency is higher than the first frequency by a multiple of at least one of 2, 5, 10, 20, 50, and 100.
23 . The computer readable media of claim 20 , wherein impedance includes at least one of a resistive component, a reactive component, and a phase angle.
24 . The computer readable media of claim 20 , wherein the instructions further direct the processor to determine a concentration of an analyte within the sample fluid based in part on the hematocrit value.
25 . The computer readable media of claim 24 , wherein the analyte is glucose.
26 . The computer readable media of claim 25 , wherein the sample fluid includes an enzyme of at least one of glucose oxidase and glucose dehydrogenase and a mediator of at least one of potassium ferricyanide and hexaammineruthenium chloride.
27 . The computer readable media of claim 20 , wherein the instructions further direct the processor to determine a calibration curve based on one or more hematocrit values.
28 . The computer readable media of claim 20 , wherein the instructions further direct the processor to output a signal representing the hematocrit value to a display.
29 . The computer readable media of claim 20 , wherein the instructions further direct the processor to apply the first pulse following application of the second pulse.
30 . A test strip for determining a hematocrit value and a glucose value of a blood sample, comprising:
a sample chamber configured to test a blood sample, wherein the chamber includes an aperture configured to receive the sample;
a first set of electrodes configured to apply a first excitation to determine a hematocrit value of the sample, wherein the first set of electrodes are generally free of reagents;
a second set of electrodes configured to apply a second excitation to determine a glucose value of the sample, wherein at least one of the second set of electrodes is located downstream of at least one of the first set of electrodes;
a reagent layer, wherein the layer substantially covers at least one of the second set of electrodes.
31 . The test strip of claim 30 , wherein at least one of the first set of electrodes and at least one of the second set of electrodes is the same electrode.
32 . The test strip of claim 30 , wherein the reagent layer includes an enzyme of at least one of glucose oxidase and glucose dehydrogenase and a mediator of at least one of potassium ferricyanide and hexaammineruthenium chloride.