Accurate analyte measurements for electrochemical test strip based on sensed physical characteristic(s) of the sample containing the analyte
Various embodiments for methods and systems that allow for a more accurate analyte concentration with a biosensor by determining at least one physical characteristic of the sample containing the analyte and deriving one of a batch slope, sampling time, or combinations thereof to attain accurate glucose concentration.
1. A method of determining an analyte concentration from a fluid sample having an analyte of interest with a biosensor having at least two electrodes and a reagent disposed on at least one electrode of the at least two electrodes, the method comprising the steps of:
a) depositing the fluid sample on any one of the at least two electrodes to start an analyte test sequence;
b) applying a first signal to the fluid sample in order to derive a hematocrit level of the fluid sample;
c) obtaining the hematocrit level of the fluid sample;
d) specifying a sampling time based on the obtained hematocrit level;
e) driving a second signal to the fluid sample, wherein the second signal is applied from the start of the analyte test sequence;
f) measuring an output signal at the specified sampling time from at least one electrode of the at least two electrodes; and
g) using a processor, calculating the analyte concentration of the fluid sample based on the measured output signal, wherein the biosensor is a test strip and the specified sampling time is either:
i) calculated using an empirically derived equation of the form:
SpecifiedSamplingTime= x 1 H x 2 +x 3
where
“SpecifiedSamplingTime” is designated as a time point in seconds from the start of the test sequence at which to sample the output signal of the test strip,
H represents the hematocrit level of the sample expressed as whole percentages;
x 1 is 4.3×10 5 (s)+/−10%;
x 2 is −3.9+/−10%; and
x 3 is 4.8 (s)+/−10%, or
ii) the specified sampling time is estimated using a stored look-up Table 1 based on the hematocrit level, expressed as whole percentages as follows:
TABLE 1
Hematocrit Level
Sampling Time (T)
(%)
(seconds)
30
5.56
31
5.46
32
5.38
33
5.32
34
5.26
35
5.2
36
5.16
37
5.12
38
5.08
39
5.06
40
5.02
41
5
42
5
43
4.98
44
4.96
45
4.96
46
4.94
47
4.92
48
4.92
49
4.9
50
4.9
51
4.9
52
4.88
53
4.88
54
4.88
55
4.86
and wherein the analyte is glucose and in which the method further comprises the step of annunciating the analyte concentration of the fluid sample.
2. The method of claim 1 , in which the steps of applying the first signal and the driving of the second signal is in sequential order.
3. The method of claim 1 , in which the step of applying of the first signal overlaps with the step of driving of the second signal.
4. The method of claim 1 , in which the step of applying of the first signal comprises the steps of directing an alternating signal to the sample so that the hematocrit level of the fluid sample is determined from an output of the alternating signal.
5. The method of claim 4 , in which the step of directing comprises the step of driving first and second alternating signals at different respective frequencies in which a first frequency is lower than a second frequency.
6. The method of claim 5 , in which the first frequency is at least one order of magnitude lower than the second frequency.
7. The method of claim 6 , in which the first frequency comprises any frequency in the range of 10 kHz to 250 kHz.
8. The method of claim 1 , in which the step of calculating of the analyte concentration is computed using the processor with an equation of the form:
G
0
=
[
I
E
-
Intercept
Slope
]
where
G 0 represents the analyte concentration of the fluid sample;
I E represents, or is, a signal value or measurement proportional to analyte concentration measured at the SpecifiedSamplingTime, quoted in nA;
Slope represents the value obtained from calibration testing of a batch of test strips of which this particular strip comes from, quoted in nA(mg/dL); and
Intercept represents the value obtained from calibration testing of a batch of test strips of which this particular strip comes from, quoted in nA.
9. The method according to claim 1 , the method further comprising the steps of:
using the processor, deriving a batch slope for the biosensor based on the hematocrit level from the obtaining step,
wherein the calculating of the analyte concentration is based on the measured output signal at the specified sampling time and the derived batch slope, and
wherein the biosensor is a test strip from a batch of test strips and the batch slope is defined as the measured or derived gradient of the line of best fit for a graph of measured glucose concentration plotted against actual glucose concentration for the batch of test strips.
10. The method of claim 9 , in which the derived batch slope is determined using the processor from an empirically derived equation of the form:
NewSlope= aH 2 bH+c
where
NewSlope represents the derived batch slope (measured in arbitrary units);
H is the measured or estimated hematocrit level of the fluid sample (measured as percent);
a is 1.4×10 −6 +/−10%,
b is −3.8×10 −4 +/−10%,
c is 3.6×10 −2 +/−10%.
11. The method of claim 10 , in which the step of calculating the analyte concentration is computed with an equation of the form:
G
0
=
[
I
E
-
Intercept
N
e
w
S
l
o
p
e
]
where
G 0 represents the analyte concentration;
I E represents a signal proportional to analyte concentration measured at the SpecifiedSamplingTime, quoted in nA;
NewSlope represents the value derived from the measured or estimated physical characteristic; and
Intercept represents the value obtained from calibration testing of the batch of test strips of which this particular strip comes from, quoted in nA.
12. A glucose meter comprising:
a housing;
a test strip port connector configured to connect to the respective electrode connectors of the test strip; and
the processor configured to perform steps b) to g) of the method of claim 1 .
13. The glucose meter of claim 12 , wherein the processor is further programmed to determine the analyte concentration of the sample based on the specific sampling time within 10 seconds of a start of the analyte test sequence.
14. A glucose measurement system comprising:
a test strip including:
a substrate; and
a plurality of electrodes connected to respective electrode connectors; and
the glucose meter according to claim 12 .