Transcutaneous analyte sensors and monitors, calibration thereof, and associated methods
Systems and methods are provided to calibrate an analyte concentration sensor within a biological system, generally using only a signal from the analyte concentration sensor. For example, at a steady state, the analyte concentration value within the biological system is known, and the same may provide a source for calibration. Similar techniques may be employed with slow-moving averages. Variations are disclosed.
1. A method of calibrating an analyte concentration sensor within a biological system, using only a signal from the analyte concentration sensor, wherein at a first repeatable event, the analyte concentration value within the biological system is known, comprising:
on a monitoring device, detecting when an analyte concentration value as measured by an analyte concentration sensor indwelling in a biological system constitutes a first repeatable event; and
on the monitoring device or on a device or server operatively coupled to the monitoring device, correlating a measurement of the analyte concentration value when the biological system is at the detected first repeatable event to the known analyte concentration value, wherein the correlating includes determining a functional relationship between the sensor reading and the known analyte concentration value, wherein the functional relationship includes a multiplicative constant, wherein the first repeatable event is selected from the group consisting of a steady-state, a post prandial rise, a daily high-low glucose spread, a decay rate, and a rate of change.
2. The method of claim 1 , wherein the detecting includes waiting a predetermined time following entry of an event on the monitoring device.
3. The method of claim 2 , wherein the event is a meal or exercise.
4. The method of claim 1 , further comprising:
following the correlating, detecting the occurrence of a second repeatable event, the second repeatable event different than the first repeatable event; and
recalibrating the analyte concentration sensor by correlating a sensor reading when the biological system is at the detected second repeatable event to the known analyte concentration value.
5. The method of claim 4 , wherein the sensor reading has a first raw value at initial calibration and a second raw value at re-calibration, and wherein the first and second raw values are different.
6. The method of claim 5 , further comprising:
following the correlating, displaying a graph or table indicating currently measured and historic values of the analyte concentration as calibrated based at least in part on the correlating; and
following the recalibration, updating the display of the graph or table indicating currently measured and historic values of the analyte concentration according to the recalibration.
7. The method of claim 6 , wherein the updating changes the display of the historic values of the analyte concentration.
8. The method of claim 5 , further comprising:
determining a difference between the first and second raw value; and
comparing a quantity based on the difference to a predetermined criteria, and based on the comparing, determining if the sensor calibration has drifted.
9. The method of claim 8 , further comprising determining a quantitative amount that the sensor calibration has drifted.
10. The method of claim 9 , further comprising adjusting the sensor calibration based on the determined quantitative amount.
11. The method of claim 8 , wherein the quantity is the slope between the first and second raw value.
12. The method of claim 11 , wherein if the slope exceeds a predetermined threshold, prohibiting future calibrations until the slope no longer exceeds a predetermined threshold.
13. The method of claim 12 , further comprising prompting a user to enter a measured value.
14. The method of claim 4 , wherein the recalibrating is configured to occur at a time when a sensor reading is substantially stable, or within a predetermined range of readings for a threshold period of time, whereby an occurrence of unexpected jumps in readings is reduced.
15. The method of claim 1 , wherein the sensor is a glucose sensor.
16. The method of claim 1 , further comprising:
subsequent to the correlating, receiving a signal from the sensor; and
displaying a value corresponding to the received signal, the displayed value based on the received signal and the known analyte concentration value.
17. The method of claim 1 , further comprising determining the known analyte concentration value by prompting the user to enter a measured value.
18. The method of claim 1 , further comprising determining the known analyte concentration value by accessing a population average.
19. An analyte sensor system, comprising:
an analyte concentration sensor configured for use within a biological system, wherein the analyte concentration sensor is configured to be calibrated using only a signal from the analyte concentration sensor, wherein at a steady state the analyte concentration value within the biological system is known;
a monitoring device, wherein the monitoring device is configured to detect when an analyte concentration value as measured by the analyte concentration sensor indwelling in a biological system constitutes a first repeatable event; and
a processor, wherein the processor is a component of the monitoring device or of a device or a server operatively coupled to the monitoring device, wherein the processor is configured to correlate a measurement of the analyte concentration value when the biological system is at the detected first repeatable event to the known analyte concentration value, wherein the correlating includes determining a functional relationship between the sensor reading and the known analyte concentration value, wherein the functional relationship includes a multiplicative constant, wherein the first repeatable event is selected from the group consisting of a steady-state, a post prandial rise, a daily high-low glucose spread, a decay rate, and a rate of change.
20. The system of claim 19 , wherein the repeatable event is selected from the group consisting of a steady-state, a post prandial rise, a daily high-low glucose spread, a decay rate, and a rate of change.
21. The system of claim 19 , wherein the processor is further configured to detect, after correlating, the occurrence of a second repeatable event, the second repeatable event different than the first repeatable event, after; and wherein the processor is further configured to recalibrate the analyte concentration sensor by correlating a sensor reading when the biological system is at the detected second repeatable event to the known analyte concentration value.
22. The system of claim 21 , wherein the processor is configured such that recalibrating occurs at a time when a sensor reading is substantially stable, or within a predetermined range of readings for a threshold period of time, whereby an occurrence of unexpected jumps in readings is reduced.