Accuracy of Continuous Glucose Sensors

Abstract

A method, apparatus, and a kit are capable of improving accuracy of CGS devices using dynamic outputs of continuous glucose sensors.

1 . A method for improving accuracy of a continuous glucose sensor (CGS), comprising:
 calibrating the CGS at a first time; and   calibrating the CGS at a second time that is determined based upon at least one of a dynamically monitored CGS value and a rate of CGS change.   
     
     
         2 . The method of  claim 1 , wherein the dynamically monitored CGS value differs by at least 15 mg/dl before the second calibration takes place. 
     
     
         3 . The method of  claim 1 , wherein the dynamically monitored CGS value differs by at least 20 mg/dl before the second calibration takes place. 
     
     
         4 . The method of  claim 1 , wherein the dynamically monitored CGS value differs by at least 30 mg/dl before the second calibration takes place. 
     
     
         5 . The method of  claim 1 , further comprising:
 dynamically monitoring the CGS value and the rate of CGS change over time.   
     
     
         6 . The method of  claim 5 , further comprising:
 calculating the first order time derivative of the monitored CGS value;   determining whether the absolute value of the first time derivative of the CGS value is substantially less than 1; and   maintaining the calibration of the CGS at the first time when the absolute value of the first time derivative of the CGS value is substantially less than 1.   
     
     
         7 . The method of  claim 6 , further comprising:
 determining the absolute change between the CGS at the second time and the CGS at the first time calibration is greater than a pre-determined value when the absolute value of the first time derivative of the CGS value is substantially less than 1; and   maintaining the calibration of the CGS at the first time when the absolute change between the CGS at the second time and the CGS at the first time calibration is greater than a pre-determined value.   
     
     
         8 . The method of  claim 7 , wherein the predetermined value is 30 mg/dl. 
     
     
         9 . The method of  claim 7 , wherein the predetermined value is 40 mg/dl. 
     
     
         10 . The method of  claim 7 , further comprising:
 recalibrating the CGS when it is determined that the absolute change between the CGS at the second time and the CGS at the first time calibration is greater than a pre-determined value.   
     
     
         11 . The method of  claim 1 , further comprising:
 improving the accuracy of the CGS output by remedying a physiology time lag between the blood glucose level and a glucose level in an interstitial fluid that interacts with the blood glucose.   
     
     
         12 . The method of  claim 11 , wherein the step of improving the accuracy further comprises:
 deriving a mathematical equation describing a time dependence of CGS output on the blood glucose level;   deriving the time dependence blood glucose level as a function of the CGS output; and   applying the derived time dependence blood glucose level function to a set of CGS raw outputs so as to predict the blood glucose level at a later time or correcting the CGS output.   
     
     
         13 . The method of  claim 12 , wherein the mathematical equation is derived based on a model that includes a description of a diffusion interaction between the blood glucose and glucose in the interstitial fluid. 
     
     
         14 . The method of  claim 12 , wherein the mathematical equation is derived based on a model that includes a description of an assumption of the glucose in the interstitial fluid. 
     
     
         15 . The method of  claim 1 , wherein the second time that is determined based upon both of the dynamically monitored CGS value and the rate of CGS change. 
     
     
         16 . A method for improving the accuracy of a continuous glucose sensor, comprising:
 calibrating the continuous glucose sensor using first blood glucose value and second blood glucose value;   measuring the first blood glucose value when the continuous glucose sensor measures a corresponding first interstitial glucose value; and   measuring the second blood glucose value when the continuous glucose sensor measures a corresponding second interstitial glucose value that is different from the first interstitial glucose value by a predetermined amount.   
     
     
         17 . The method of  claim 16 , wherein the predetermined amount is at least 15 mg/dl. 
     
     
         18 . The method of  claim 16 , wherein the predetermined amount is at least 20 mg/dl. 
     
     
         19 . The method of  claim 17 , wherein the first and second glucose data are obtained at different times. 
     
     
         20 . The method of  claim 17 , wherein the second glucose data is obtained through a decision making loop that comprises a determination of a rate of CGS change based on a pre-determined criterion. 
     
     
         21 . The method of  claim 20 , wherein the pre-determined criterion states that if the rate of CGS change is equal to or greater than a pre-determined value, maintaining the CGS calibration with the first glucose data. 
     
     
         22 . The method of  claim 21 , wherein the pre-determined value is 1. 
     
     
         23 . The method of  claim 22 , wherein the pre-determined criterion further states that if the rate of CGS change is less than 1, performing another decision based on another predetermined value. 
     
     
         24 . The method of  claim 23 , wherein said another pre-determined criterion states that if the absolute difference between the CGS and the calibrated CGS with the first blood glucose data is equal to or less than a pre-determined difference value, maintaining the CGS calibration with the first glucose data. 
     
     
         25 . The method of  claim 24 , wherein said another pre-determined criterion further states that if the absolute difference between the CGS and the calibrated CGS with the first blood glucose data is greater than the pre-determined difference value, performing another calibration with the second blood glucose data. 
     
     
         26 . The method of  claim 17 , further comprising:
 improving the accuracy of the CGS output by remedying a physiology time lag between the blood glucose level and a glucose level in an interstitial fluid that interacts with the blood glucose.   
     
     
         27 . The method of  claim 26 , wherein the step of improving the accuracy further comprises:
 deriving a mathematical equation describing a time dependence of CGS output on the blood glucose level;   deriving the time dependence blood glucose level as a function of the CGS output; and   applying the derived time dependence blood glucose level function to a set of CGS raw outputs so as to correct the CGS output for inherent time lags.   
     
     
         28 . The method of  claim 27 , wherein the mathematical equation is derived based on a model that includes a description of a diffusion interaction between the blood glucose and glucose in the interstitial fluid. 
     
     
         29 . The method of  claim 27 , wherein the mathematical equation is derived based on a model that includes a description of an assumption of the glucose in the interstitial fluid. 
     
     
         30 . The method of  claim 27 , wherein the time dependence blood glucose level as a function of the CGS output is an inversed function of the mathematical equation that describes the time dependence of the CGS output on the blood glucose level. 
     
     
         31 . A system for improving an accuracy of a continuous glucose sensor, comprising:
 an accuracy improving module accessible to an output of the continuous glucose sensor, further comprising:
 a decision making mechanism capable of determining a calibration at a time based upon at least one of a dynamically monitored output of the continuous glucose sensor. 
   
     
     
         32 . The system of  claim 31 , wherein the decision making mechanism is capable of determining the calibration at the time that is based upon the output of the continuous glucose sensor and a rate of change of the output of the continuous glucose sensor. 
     
     
         33 . The system of  claim 31 , wherein the accuracy improving module further comprises:
 an initial request module capable of initiating a calibration at a predetermined time sequence.   
     
     
         34 . The system of  claim 33 , wherein the decision making mechanism further comprises:
 a monitoring module capable of dynamically monitoring the output from the continuous glucose sensor.   
     
     
         35 . The system of  claim 34 , wherein the decision making mechanism further comprises:
 a determination instruction stating that the dynamically monitored output from the continuous glucose sensor differs by at least 15 mg/dl before the second calibration takes place.   
     
     
         36 . The system of  claim 34 , wherein the decision making mechanism further comprises:
 a determination instruction stating that the dynamically monitored output from the continuous glucose sensor differs by at least 20 mg/dl before the second calibration takes place.   
     
     
         37 . The system of  claim 34 , wherein the decision making mechanism further comprises:
 a determination instruction stating that the absolute rate of change is substantially equal to or greater than 1 before the second calibration takes place.   
     
     
         38 . The system of  claim 34 , further comprising:
 a time lag correction module capable of improving the accuracy of the CGS output by remedying a physiology time lag between the blood glucose level and a glucose level in an interstitial fluid that interacts with the blood glucose.   
     
     
         39 . A kit, comprising
 a continuous glucose sensor;   a calibration unit in a data communication with to the continuous glucose sensor for calibrating the continuous glucose sensor; and   a set of instructions including instructions for instruction monitoring monitored output from the continuous glucose sensor, and performing first and second calibrations at first and second continuous glucose sensor output values that differ by at least 15 mg/dl.   
     
     
         40 . The kit of  claim 39 , wherein the calibration unit is connectable to the continuous glucose sensor. 
     
     
         41 . The kit of  claim 39 , wherein the calibration unit is an integral member of the continuous glucose sensor. 
     
     
         42 . The kit of  claim 39 , wherein the instruction further states that the dynamically monitored output of the continuous glucose sensor differs by at least 20 mg/dl before the second calibration takes place. 
     
     
         43 . The kit of  claim 39 , wherein the instruction further states that an absolute rate of change of the output of the continuous glucose sensor is less than 1 before the second calibration takes place. 
     
     
         44 . The kit of  claim 39 , wherein the accuracy improving mechanism further comprises:
 a time lag correction module accessible to the output of the continuous glucose sensor and capable of remedying a physiology time lag.   
     
     
         45 . A method for improving an accuracy of a continuous glucose sensor, comprising:
 calibrating the CGS using a first blood glucose level and a second blood glucose level different by a predetermined amount from the first glucose data.   
     
     
         46 . The method of  claim 45 , wherein the predetermined amount is at least 15 mg/dl. 
     
     
         47 . The method of  claim 46 , wherein the predetermined amount is at least 20 mg/dl. 
     
     
         48 . The method of  claim 47 , wherein the second glucose data is obtained through a decision making loop that comprises a determination of a rate of CGS change based on a pre-determined criterion. 
     
     
         49 . The method of  claim 48 , wherein the pre-determined criterion states that if the rate of CGS change is equal to or greater than 1, maintaining the CGS calibration with the first glucose data. 
     
     
         50 . A computer-readable medium having computer executable instructions for performing the method set forth in  claim 1 . 
     
     
         51 . A computer-readable medium having computer executable instructions for performing the method set forth in  claim 16 . 
     
     
         52 . A computer-readable medium having computer executable instructions for performing the method set forth in  claim 45 . 
     
     
         53 . A kit, comprising:
 a calibration unit for calibrating a continuous glucose, the calibration unit comprising a blood glucose sensor; and   a set of instructions including instructions for monitoring output from a continuous glucose sensor, and performing first and second calibrations at first and second continuous glucose sensor output values that differ by at least 15 mg/dl, where the first and second calibrations comprise respectively first and second determinations of blood glucose with the blood glucose sensor.