Glucose management indicator may be calculated with as little as 7 days of CGM data
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Glucose management indicator — an estimate of HbA1c based on continuous glucose monitoring information — may be accurately calculated for adults with type 1 or type 2 diabetes using as few as 7 days of CGM data, according to researchers.
“Minimal differences were observed between glucose management indicator (GMI) computed using 14 days of data compared with GMI computed with 7 days,” Peter Calhoun, PhD, a biostatistician at the Jaeb Center for Health Research in Tampa, Florida, and colleagues wrote in a brief report published in Diabetes Technology & Therapeutics. “Larger differences were present when GMI was based on 5 or fewer days.”
Calhoun and colleagues conducted an analysis from five clinical trials: REPLACE-BG T1D, HypoDE T1D, DIAMOND T1D, DIAMOND T2D and MOBILE T2D. Participants in the trials with at least 14 days of CGM data in the 20 days before outcome visits at 6 or 8 months were included. All five trials used the Dexcom G4, G5 or G6 sensors. GMI was computed for each participant using 14 days of data. Researchers also computed GMI using 1 to 13 days of data. Absolute differences in GMI values and Pearson correlation coefficients between the 14-day GMI and GMI calculated with 1 to 13 days of data were computed.
Data from 581 adults were included in the analysis (mean age, 49 years; mean HbA1c, 7.3%); 435 had type 1 diabetes and 146 had type 2 diabetes. The 14-day GMI was strongly correlated with 10 days of data (r = 0.98) and 7 days of data (r = 0.95). Correlation was lower with 5 days of data (r = 0.91) and 3 days of data (r = 0.86).
The mean absolute difference in GMI was 0.08% between 14 days and 10 days of data, 0.13% between 14 days and 7 days of data, 0.17% between 14 days and 5 days of data and 0.24% between 14 days and 3 days of data. The proportion of GMI values within 0.3% of the 14-day GMI reading was 98% with 10 days of data, 87% with 7 days of data, 77% with 5 days of data and 60% with 3 days of data.
“Analyses only included adult participants wearing a real-time CGM, but we expect results to generalize to other participants assuming that the CGM data were collected during a period of stable glucose control,” the researchers wrote. “These data indicate that a reasonable estimate of HbA1c with the GMI can be obtained with 7 days of CGM data in ambulatory glucose profile reports, although 14 or more days is preferred.”
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