Objective: Continuous glucose monitoring (CGM) has emerged as a key component of diabetes care but there are issues with data synthesis and application. A published regression equation converts CGM-derived mean glycemia into an estimate of laboratory-measured HbA1c, termed glucose management indicator (GMI). How the GMI formula defers by CGM device is not known. We compared the GMI derived from published formula vs. GMI derived from FreeStyle Libre specific regression equation.

Research Design and Methods: We conducted an observational study using EHR data from a single academic endocrinology practice (Tufts Medical Center, Boston, MA). We included data from patients with diabetes and a minimum of 10-days of sensor data collected with FreeStyle Libre Pro or Personal, immediately prior to measurement of HbA1c. We plotted HbA1c and Libre average glucose and derived a Libre specific regression equation. We compared the GMI derived from the published formula (GMIp) with the Libre-specific GMI (GMIL).

Results: Data were available from 59 patients (age 62 [range 22-90], 36% women, BMI 29 Kg/m2; 80% had type 2 diabetes; 70% had diabetes ≥10 years disease; HbA1c 8.1% (range 4.8-13.7). The mean number of days with CGM data was 28 (range 10-90). The Libre specific regression equation formula was GMI (%) = 5.04 + 0.0173*(mean glucose in mg/dL)]. Mean GMIp was 8.1% (SD 0.9) and mean GMIL was 7.6% (SD 1.3)(p=0.004).

Conclusion: The GMI derived from a device-specific regression equation differs from the published GMI. The development of a device specific GMI may be warranted.


E. Angellotti: None. S. Muppavarapu: None. R. Siegel: None. A.G. Pittas: None.

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