Transient signal error trap for an analyte measurement determined from a specified sampling time derived from a sensed physical characteristic of the sample containing the analyte
Various embodiments for methods, systems, and meters that allow for a more accurate analyte concentration with a biosensor by determining at least one physical characteristic of the sample and determining whether at least one output transient signal of the biosensor is erroneous by monitoring the biosensor and flagging an error if the signal outputs of the biosensor do not meet certain criteria.
1. An analyte measurement system comprising:
a test strip including:
a substrate;
a plurality of electrodes connected to respective electrode connectors; and
an analyte meter including:
a housing;
a test strip port connector configured to connect to the respective electrode connectors of the test strip; and
a microprocessor in electrical communication with the test strip port connector to apply electrical signals or sense electrical signals from the plurality of electrodes, wherein the microprocessor is programmed to:
(a) apply a first signal to the plurality of electrodes so that a physical characteristic of a fluid sample is determined wherein the physical characteristic is one of viscosity or hematocrit;
(b) estimate an analyte concentration based on a predetermined sampling time point during a test sequence;
(c) apply a second signal to a first electrode and a second electrode of the plurality of electrodes at a specified sampling time point or interval during the test sequence dictated by the determined physical characteristic;
(d) measure a signal output at a plurality of time points including the specified sampling time for each of the first and second electrodes;
(e) measure a signal output at a predetermined offset time interval (Δt) from the specified sampling time for each of the first and second electrodes;
(f) evaluate, for each of the first and second electrodes, whether a slope of the signal outputs between the predetermined offset time interval (Δt) and the specified sampling time is approximately zero or increasing over time;
(g) if the slope of the signal output for each electrode at the predetermined offset time (Δt) to the specified sampling time is decreasing then determine or calculate the analyte concentration from the signal outputs of the first and second electrodes at the specified sampling time and annunciate the analyte concentration; and
(h) if the slope of the signal output for each electrode at the predetermined offset (Δt) time to the specified sampling time is approximately zero or increasing over time then annunciate an error.
2. The system of claim 1 , in which the first, second, third and fourth electrodes are disposed in the same chamber provided on the substrate.
3. The system of claim 1 , in which the plurality of electrodes comprises four electrodes with the first and second electrodes to measure the analyte concentration and third and fourth electrodes to measure the physical characteristic.
4. The system of claim 3 , in which the first and second electrodes and third and fourth electrodes are disposed in respective two different chambers provided on the substrate.
5. The system of claim 3 , in which all of the electrodes are disposed on the same plane defined by the substrate.
6. The system of claim 3 , in which a reagent is disposed proximate the at least two other electrodes and no reagent is disposed on the at least two electrodes.
7. The system of claim 3 , in which the analyte concentration is determined from the second signal within about 10 seconds of a start of the test sequence and the predetermined offset time interval (Δt) comprises any value from about +0.1 second to about +0.6 seconds or about −0.1 second to about −0.6 second.
8. The system of claim 3 , in which the specified sampling time is selected from a look-up table that includes a matrix in which different qualitative categories of the estimated analyte are set forth in the leftmost column of the matrix and different qualitative categories of the measured or estimated physical characteristic are set forth in the topmost row of the matrix and the sampling times are provided in the remaining cells of the matrix.
9. An analyte measurement system comprising:
a test strip including:
a substrate;
a plurality of electrodes connected to respective electrode connectors; and
an analyte meter including:
a housing;
a test strip port connector configured to connect to the respective electrode connectors of the test strip; and
a microprocessor in electrical communication with the test strip port connector to apply electrical signals or sense electrical signals from the plurality of electrodes, wherein the microprocessor is programmed to:
(a) apply a first signal to the plurality of electrodes so that a physical characteristic of a fluid sample is determined wherein the physical characteristic is one of viscosity or hematocrit;
(b) estimate an analyte concentration based on a predetermined sampling time point during a test sequence;
(c) apply a second signal to a first electrode and a second electrode of the plurality of electrodes at a specified sampling time point or interval during the test sequence dictated by the determined physical characteristic;
(d) measure a signal output at a plurality of time points including the specified sampling time for each of the first and second electrodes;
(e) evaluate, for each of the first and second electrodes, whether a slope of the signal outputs between the predetermined offset time interval and the specified sampling time is approximately zero or increasing over time;
(f) if the slope of the signal output for each electrode at the predetermined offset time to the specified sampling time is approximately zero or increasing over time then set an error flag as active;
(g) determine or calculate the analyte concentration from the signal outputs of the first and second electrodes at the specified sampling time;
(h) if the error flag is set then terminate the process; and
(i) if the slope of the signal output for each electrode at the predetermined offset time to the specified sampling time is decreasing then annunciate the analyte value.
10. The system of claim 9 , in which the slope for each working electrode is defined by the respective equations:
m
1
=
I
we
1
(
@
Tss
)
-
I
we
1
(
@
Δ
t
+
Tss
)
Tss
-
(
Tss
-
Δ
t
)
m
2
=
I
we
2
(
@
Tss
)
-
I
we
2
(
@
Δ
t
+
Tss
)
Tss
-
(
Tss
-
Δ
t
)
where
I we1(Δt+Tss) is the output signal proximate time point defined by (Tss+Δt);
Tss is the specified sampling time and Δt is a positive or negative time differential, and preferably about −30 milliseconds;
I we2(Δt+Tss) is the output signal proximate time point defined by (Tss+Δt);
Tss is the specified sampling time and Δt is a positive or negative time differential, and preferably about −30 milliseconds;
I we1(Tss) is the output signal proximate the specified sampling time Tss;
I we2(Tss) is the output signal proximate the specified sampling time Tss;
Δt comprises a predetermined time interval from about ±100 milliseconds to ±600 milliseconds;
m 1 is an estimate of the slope of the output signals for the first working electrode proximate the specified sampling time;
m 2 is an estimate of the slope of the output signals for the second working electrode proximate the specified sampling time.
11. An analyte measurement system comprising:
a test strip including:
a substrate;
a plurality of electrodes connected to respective electrode connectors; and
an analyte meter including:
a housing;
a test strip port connector configured to connect to the respective electrode connectors of the test strip; and
a microprocessor in electrical communication with the test strip port connector to apply electrical signals or sense electrical signals from the plurality of electrodes, wherein the microprocessor is programmed to:
(a) apply a first signal to the plurality of electrodes so that a physical characteristic of a fluid sample is determined wherein the physical characteristic is one of viscosity or hematocrit;
(b) estimate an analyte concentration based on a predetermined sampling time point during a test sequence;
(c) apply a second signal to a first electrode and a second electrode of the plurality of electrodes at a specified sampling time point or interval during the test sequence dictated by the determined physical characteristic;
(d) measure a signal output at a plurality of time points including the specified sampling time for each of the first and second electrodes;
(e) measure a signal output at a predetermined offset time interval (Δt) from the specified sampling time for each of the first and second electrodes;
(f) evaluate whether the magnitude of the output signal for each working electrode at the predetermined offset time interval from the specified sampling time greater or equal than the magnitude of the measured or sampled output signal of the working electrode at the specified sampling time and if true calculate an analyte concentration for the sample otherwise if false annunciate an error or set an error flag; and
(g) determine whether the magnitude of the output signal for each working electrode at an offset time interval before the specified sampling as less than the magnitude for the working electrode at the specified sampling time Tss and if true annunciate an error or set an error flag active.
12. An analyte measurement system comprising:
a test strip including:
a substrate;
a plurality of electrodes connected to respective electrode connectors; and
an analyte meter including:
a housing;
a test strip port connector configured to connect to the respective electrode connectors of the test strip; and
a microcontroller in electrical communication with the test strip port connector to apply electrical signals or sense electrical signals from the plurality of electrodes, wherein the microcontroller is programmed to:
(a) apply a first signal to the plurality of electrodes so that a physical characteristic of the fluid sample is determined wherein the physical characteristic is one of viscosity or hematocrit;
(b) estimate an analyte concentration based on a predetermined sampling time point during a test sequence;
(c) apply a second signal to first and second electrodes of the plurality of electrodes;
(d) calculate a specified sampling time based on the physical characteristic of the sample in which the specified sampling time
is designated as a time point from the start of the test sequence at which to sample the output signal of the test strip;
(e) measure output signals from the first and second electrodes at the specified sampling time during the test sequence;
(f) evaluate, for each of the first and second electrodes, whether a slope of the signal outputs between the predetermined offset time interval and the specified sampling time is approximately zero or increasing over time;
(g) if the slope of the signal output for each electrode at the predetermined offset time to the specified sampling time is decreasing then determine or calculate the analyte concentration from the signal outputs of the first and second electrodes at the specified sampling time and annunciate the analyte concentration;
(h) if the slope of the signal output for each electrode at the predetermined offset time to the specified sampling time is approximately zero or increasing over time then annunciate an error.
13. The system of claim 12 , in which the microcontroller determines the analyte concentration with an equation of the form:
G
0
=
[
I
T
-
Intercept
Slope
]
where
G 0 represents an analyte concentration;
I T represents the output signals measured at the specified sampling time;
Slope represents the value obtained from calibration testing of a batch of test strips of which this particular strip comes from; and
Intercept represents the value obtained from calibration testing of a batch of test strips of which this particular strip comes from.
14. The system of claim 12 , in which the microcontroller estimates the analyte concentration with an equation of the form:
G
est
=
(
I
E
-
x
2
)
x
1
where G est represents the estimated analyte concentration;
I E is the signal measured at about 2.5 seconds;
x 1 comprises a calibration slope of a particular batch of biosensors;
x 2 comprises a calibration intercept of a particular batch of biosensors; and
in which the microcontroller determines the analyte concentration with an equation of the form:
G
o
=
(
I
s
-
x
4
)
x
3
where: G O represents the analyte concentration;
I S comprises the signal measured at the specified sampling time;
x 3 comprises a calibration slope of a particular batch of biosensors; and
x 4 comprises the intercept of a particular batch of biosensors.
15. The system of claim 14 , in which the plurality of electrodes comprises four electrodes with the first and second electrodes to measure the analyte concentration and third and fourth electrodes to measure the physical characteristic.
16. The system of claim 15 , in which the first, second, third and fourth electrodes are disposed in the same chamber provided on the substrate.
17. The system of claim 15 , in which the first and second electrodes and third and fourth electrodes are disposed in respective two different chambers provided on the substrate.
18. The system of claim 15 , in which all of the electrodes are disposed on the same plane defined by the substrate.
19. The system of claim 15 , in which a reagent is disposed proximate the at least two other electrodes and no reagent is disposed on the at least two electrodes.
20. The system of claim 15 , in which the analyte concentration is determined from the second signal within about 10 seconds of a start of the test sequence and the predetermined offset time interval Δt comprises any value from about 10 milliseconds to about 60 milliseconds.