Glucose Management Indicator (GMI): Insights and Validation Using Guardian 3 and Navigator 2 Sensor Data

The glucose management indicator (GMI) is an updated approach for estimating HbA1c from continuous glucose monitoring (CGM) data (1). GMI is calculated using the formula GMI (%) = 3.31 + 0.02392 × mean glucose in mg/dL, which has been derived by regressing contemporaneously measured HbA1c values ( y -axis) against mean sensor glucose levels ( x -axis). GMI was conceived using data collected solely with Dexcom glucose sensors; thus, generalization and validation of the formula for other sensor makes is currently unknown (1). Here, we assessed GMI using Guardian Sensor 3 (Guardian 3) (Medtronic Inc., Northridge, CA) and Freestyle Navigator II (Navigator 2) (Abbott Diabetes Care, Alameda, CA) glucose sensors and evaluated the difference between GMI and laboratory-measured HbA1c values.We used data from three recently published 12-week randomized controlled trials evaluating the safety and effectiveness of closed-loop in comparison with sensor-augmented pump therapy in adults and children with type 1 diabetes and HbA1c between 7.5% and 10% (58 and 86 mmol/mol): APCam11 (Home Testing of Day and Night Closed Loop With Pump Suspend Feature) ( n = 86, Guardian 3) (2), AP@home04 (Closing the Loop in Adults With Sub-optimally Controlled Type …