A Comparative Analysis Between Original and Updated Glucose Management Indicator and Glycated Haemoglobin Across Continuous Glucose Monitoring Sensors in Type 1 Diabetes

AIMS: The continuous glucose monitoring (CGM)-derived glucose management indicator (GMI) is used for estimating glycated haemoglobin (HbA1c). This study assessed agreement between GMI-calculated using both original and updated (uGMI) models-and laboratory-measured HbA1c across Dexcom, MiniMed and Abbott sensors. MATERIALS AND METHODS: Real-world data from adults with type 1 diabetes using automated insulin delivery were retrospectively analysed. Δ(GMI-HbA1c) and Δ(uGMI-HbA1c) were evaluated over 90 days preceding HbA1c (n = 383) and over 28 days preceding HbA1c (n = 375). Agreement was measured as directional difference, indicating GMI overestimation or underestimation of HbA1c, and absolute difference, indicating magnitude of agreement between GMI and HbA1c. Agreement was assessed across sensor groups using ANCOVA, adjusting for coefficient of variation and ethnicity. RESULTS: Although mean directional differences were statistically significant for Δ(GMI-HbA1c) and Δ(uGMI-HbA1c) across all sensor groups (p < 0.001), differences were small and not clinically important, 90-day adjusted means (95% CI)-Δ(GMI-HbA1c): Dexcom 0.17% (0.09, 0.25), MiniMed -0.15% (-0.28, -0.02), Abbott -0.08% (-0.25, 0.09); Δ(uGMI-HbA1c): Dexcom 0.22% (0.14, 0.30), MiniMed -0.10% (-0.23, 0.02), Abbott -0.02% (-0.19, 0.15). Mean absolute difference did not significantly differ across sensor groups-Δ(GMI-HbA1c): 0.42%-0.51% (p = 0.353), Δ(uGMI-HbA1c): 0.41%-0.52% (p = 0.221). CONCLUSIONS: GMI/uGMI performed consistently across sensor groups. Where clinically meaningful discrepancies between GMI/uGMI and HbA1c arise, these warrant interpretation within the context of individual clinical and laboratory factors rather than attribution to sensor manufacturer, reinforcing the need for personalised use of GMI alongside HbA1c.