System and method for using multiple sensor calibration methods
The present invention relates to a system and method for improving glucose sensor accuracy by utilizing multiple calibration methods and selecting the most accurate method depending on a consensus glucose concentration estimate. Embodiments of the present invention comprise the steps of performing at least one in vivo update of surrounding glucose to acquire glucose values; calculating multiple updated calibration estimates using the updated glucose values; calculating an initial consensus glucose estimate from sensor output using each updated calibration estimate; applying a smooth crossover function to the multiple calibration estimates based on the value of the initial consensus glucose estimate; and adding weights to the multiple calibration estimates to acquire a consensus glucose estimate.
1. A method for improving glucose sensor accuracy by utilizing multiple calibration estimates, the method comprising the steps of:
performing at least one in vivo update of surrounding glucose to acquire glucose values with the glucose sensor;
applying multiple calibration estimates to the updated glucose values;
calculating multiple updated calibration estimates using the updated glucose values; wherein each of the multiple calibration estimates is more accurate than the other of the multiple calibration estimates within one of a plurality of glucose concentration ranges;
calculating an initial consensus glucose estimate value from sensor output using each updated calibration estimate;
weighting the multiple updated calibration estimates based on the value of the initial consensus glucose estimate value such that the weights sum to unity, wherein the weights are smoothly shifted from zero to one among the multiple calibration estimates as a function of the initial consensus glucose estimate value in glucose concentration regions around boundaries of the plurality of glucose concentration ranges;
determining a glucose level with the glucose sensor based on a weighted multiple calibration estimates; and
displaying the determined glucose level on a display of a glucose blood measurement device.
2. The method of claim 1 , wherein the initial consensus glucose estimate is calculated by calculating a median of the multiple updated calibration estimates.
3. The method of claim 1 , further comprising determining a calibration estimate by comparative analysis of a representative set of in vivo data.
4. The method of claim 1 , further comprising setting a nocturnal hypoglycemia alarm in a glucose region between 70 to 110 mg/dL.
5. The method of claim 1 , wherein the multiple updated calibration estimates are calculated based on the equation:
S =( S 0 +S inf*Glucose/ KD )/(1+Glucose/ KD ) or
Glucose= KD *( S−S 0)/( S inf− S ), where
S=sensor output,
KD=apparent binding constant,
S0=sensor output when no glucose is present, and
Sinf=sensor output when glucose is present at saturating levels.
6. The method of claim 5 , wherein glucose level is determined based on a diffusion-based transport equation:
PG=DF *{ISFG+Tau* d (ISFG)/ dt }, where
PG=plasma glucose concentration,
ISFG=interstitial glucose concentration,
DF=in vivo dilution factor,
Tau=in vivo time constant, and
d(ISFG)/dt=the time rate of change of the interstitial glucose.
7. The method of claim 6 , wherein glucose level is determined based on an equation for plasma glucose expressed as:
PG=DF*{KD *( S−S 0)/( S inf− S )+Tau* d [ KD *( S−S 0)/( S inf− S )}]/ dt}.