An advanced algorithm was developed for the Medtronic fourth-generation glucose sensor to eliminate the need for blood glucose meter calibrations. The algorithm uses electrochemical impedance spectroscopy and other measurements to self-calibrate the sensor and adjust CGM system sensitivity over time. Self-calibration adjusts for potential sensor-to-sensor variability, as well as subject-dependent sensitivity changes over time.
The new algorithm was designed to not require self-monitored blood glucose (SMBG) input during use, but accepts calibrations at any time to improve CGM system performance. It contains multiple independent sensor glucose (SG) calculation units that implement a distinct dynamic model of interstitial glucose that accounts for differences in response caused by sensor-dependent and time-dependent nonlinearities. This approach is particularly useful during the post-sensor insertion period and during periods of hypoglycemia. Each dynamic model was selected for its unique pattern of strengths, which complement each other to augment overall performance. The output of each model is combined to provide a final SG value and a measure of confidence in the calculated value.
Performance was evaluated on 31 subjects with type 1 and type 2 diabetes against SMBG values (2441 points over 80 sensors). Sensors were inserted in the arm. The overall (7-day) mean absolute relative difference was 10.8% with no calibrations, 9.5% with 1 calibration/day. There were 86.7% of points that met the 20% agreement rate with no calibrations, 90.0% with 1 calibration/day.
A new advanced algorithm for the fourth-generation glucose sensor enables the CGM system to function with good accuracy without SMBG calibrations.
T. Engel: Employee; Self; Medtronic MiniMed, Inc. P. Ajemba: Employee; Self; Medtronic. J. Nishida: Employee; Self; Medtronic MiniMed, Inc. K. Nogueira: Employee; Self; Medtronic. B. Grosman: Employee; Self; Medtronic. A. Tsai: None. Y. Lu: None. A. Sullivan: None. A. Varsavsky: Employee; Self; Medtronic MiniMed, Inc..