Differences in the Glucose Management Indicator Between Continuous Glucose Monitoring Systems

The glucose management indicator (GMI) estimates HbA1c from continuous glucose monitoring (CGM)-derived mean glucose. We assessed whether this relationship differs between contemporary CGM systems.

In this observational study, mean sensor glucose was derived from 2 months of CGM data preceding HbA1c measurement in adults with Type 1 diabetes using Dexcom (Dx) G6/G7 (n = 252) or Medtronic Guardian 4/Simplera (GSi) (n = 180). Device-specific GMI equations were derived using linear regression of measured HbA1c on mean sensor glucose and compared with the original GMI equation. For direct comparison of the Dx and GSi GMI equations, these GMI equations were combined, with 95% confidence intervals calculated using the delta method.

The Dx GMI equation yielded statistically significantly lower GMI values compared with the original GMI equation at mean sensor glucose levels < 13.7 mmol/L, with increasing differences at lower glucose levels. Conversely, at mean sensor glucose levels above 8.3 mmol/L, the GSi GMI equation yielded statistically significantly higher GMI values than the original GMI equation, with increasing differences at higher glucose levels. The Dx and GSi device-specific GMI equations yielded statistically significantly different GMI values > 6.7 mmol/L, with increasing differences at higher glucose levels.

The relationship between mean sensor glucose and HbA1c differed between contemporary CGM systems. This finding suggests that device-specific GMI equations may improve interpretation of glycaemic control in the absence of standardisation across contemporary CGM systems.