Glucose management indicator: Do we need device-specific equations?

Area of Science:

• Endocrinology
• Medical Devices
• Diabetes Technology

Background:

• The Glucose Management Indicator (GMI) is a metric derived from continuous glucose monitoring (CGM) data used to estimate HbA1c.
• Existing GMI calculations may not be universally applicable across different CGM systems, potentially leading to inaccuracies.

Purpose of the Study:

• To develop and validate device-specific GMI equations for the Guardian 3 (G3) and Guardian 4 (G4) CGM sensors.
• To compare the performance of these new GMI equations against the original GMI.
• To analyze the glycaemic gap (HbA1c - GMI) and its relationship with HbA1c for different CGM systems.

Main Methods:

• An observational study involving adult patients with type 1 diabetes using G3 and G4 CGM devices.
• Linear mixed models were used to estimate HbA1c from CGM-derived mean glucose for both G3 and G4 sensors.
• Regression analysis and Bland-Altman plots were employed to compare device-specific GMI estimates and their residuals (gaps) with the original GMI.

Main Results:

• The study included 120 adult type 1 diabetes patients (90 G3, 30 G4) with 194 measurement points.
• For both G3 and G4 sensors, the original GMI significantly underestimated HbA1c at higher ranges.
• The GMI overestimated HbA1c in the lower range for the G4 sensor, and device-specific GMI gaps were smaller than the original GMI gap.

Conclusions:

• Device-specific GMI equations for Guardian 3 and 4 sensors can mitigate the risk of clinically significant HbA1c under- and overestimation.
• Implementing tailored GMI equations can enhance the accuracy of glycaemic assessment, leading to improved clinical decision-making for type 1 diabetes management.