The calculation of the Glucose Management Indicator (GMI) is influenced by the Continuous Glucose Monitoring system and patient race.

OBJECTIVE: To determine whether the glucose management indicator (GMI), an estimate of hemoglobin A1c (HbA1c) derived from continuous glucose monitoring (CGM) mean glycemia, differs by CGM system and patient race.
METHODS: 103 patients with prediabetes or stable diabetes and a minimum of 10 days of CGM data collected with the FreeStyle Libre CGM system immediately prior to measurement of HbA1c were included in this clinic-based observational study that used data from electronic health records in an academic endocrinology clinic. HbA1c and Libre CGM measured mean glucose were plotted to derive a race-agnostic and race-specific regression equations to calculate a Libre-specific GMI (GMILi). The mean GMI derived from the published formula (GMIP) was compared with GMILi.
RESULTS: Mean ± SD age of patients was 61.9 ± 13.3 years; 50% were of non-white race and 77% had type 2 diabetes; mean HbA1c was 62 mmol/mol (7.8%). The mean (range) number of days with available CGM data was 26 (10-90). The mean ± SD GMILi was higher than the GMIP in the entire cohort (7.9 ± 1.0% vs. 7.5 ± 1.0% respectively; p=0.01) and among Asian patients (7.9 ± 0.9% vs 7.2 ±1.0% respectively; p=0.03).
CONCLUSION: In a cohort with prediabetes or stable diabetes, the regression equation to calculate GMI varied by CGM system and patient race. The development of device- and race-specific regression equations for GMI may be warranted.