Calibration of a subcutaneous amperometric glucose sensor implanted for 7 days in diabetic patients. Part 2. Superiority of the one-point calibration method.
Calibration, i.e. the transformation in real time of the signal I(t) generated by the glucose sensor at time t into an estimation of glucose concentration G(t), represents a key issue for the development of a continuous glucose monitoring system.


OBJECTIVE
To compare two calibration procedures. In the one-point calibration, which assumes that I(o) is negligible, S is simply determined as the ratio I/G, and G(t) = I(t)/S. The two-point calibration consists in the determination of a sensor sensitivity S and of a background current I(o) by plotting two values of the sensor signal versus the concomitant blood glucose concentrations. The subsequent estimation of G(t) is given by G(t) = (I(t)-I(o))/S.


METHODS
A glucose sensor was implanted in the abdominal subcutaneous tissue of nine type 1 diabetic patients during 3 (n = 2) and 7 days (n = 7). The one-point calibration was performed a posteriori either once per day before breakfast, or twice per day before breakfast and dinner, or three times per day before each meal. The two-point calibration was performed each morning during breakfast.


RESULTS
The percentages of points present in zones A and B of the Clarke Error Grid were significantly higher when the system was calibrated using the one-point calibration. Use of two one-point calibrations per day before meals was virtually as accurate as three one-point calibrations.


CONCLUSIONS
This study demonstrates the feasibility of a simple method for calibrating a continuous glucose monitoring system.
Choleau
C
C
INSERM U341, Diabetes Department, Hôtel-Dieu Hospital, 1 Place du Parvis Notre Dame, 75004, Paris, France.
Klein
J C
JC
Reach
G
G
Aussedat
B
B
Demaria-Pesce
V
V
Wilson
G S
GS
Gifford
R
R
Ward
W K
WK
D015374:Biosensing Techniques / Q000295:instrumentation / Q000706:statistics & numerical data*; D001786:Blood Glucose / Q000032:analysis*; D015190:Blood Glucose Self-Monitoring / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D006801:Humans; D019736:Prostheses and Implants
D001786:Blood Glucose