Objective: Current consensus is that 10-14 days of continuous glucose monitoring (CGM) sampling time is adequate to assess long-term glycemic control in T1D and insulin-using T2D populations. Optimal CGM sampling duration has not been widely studied in people with T2D not using insulin. We studied the relationship between true and estimated long-term (90-day) glycemic control in people with T2D not using insulin.

Methods: The study population (N = 829) was composed of adults with T2D enrolled in Level2, a virtual specialty clinic, with CGM data on 75% (68) of the 90 days preceding an A1c lab result and no insulin fills during this period. The mean age and A1c were 56 years and 6.7% respectively. We computed the median absolute percentage error (MAPE) and Pearson correlations (R) between glycemic metrics from sampling periods of increasing duration and the full 90-day period. Because this population was at low risk for hypoglycemia glucose management indicator (GMI) and time above range (>180 mg/dL, TAR) were the primary outcomes of interest. We also assessed the correlations between GMI and A1c.

Results: GMI and TAR from 14-day measurements were highly correlated (R = 0.92) with 90-day values, increasing to R = 0.94 with 30-day measurements. Correlations of GMI and A1c were high with 14 and 30 days (R = 0.79, R = 0.82) but did not exceed R = 0.85 with longer sampling periods. MAPE was 2.2 (SD = 2.6) and 1.5 (SD = 2.1) for GMI with 14- and 30-day measurements, respectively, and 29.2 (SD = 47.4) and 21.2 (SD = 27.1) for TAR.

Conclusion: In the T2D population not using insulin, 14 days of CGM data is sufficient to estimate long-term mean glucose and the discordance with A1c is consistent with previous studies of people with T1D and insulin-using T2D. TAR is subject to greater error than in previous studies of people with T1D and insulin-using T2D and more work is needed to understand this discrepancy.

Disclosure

S.Bacon: Employee; Optum Labs, Research Support; Level2. N.Thompson: Employee; Level2, Stock/Shareholder; UnitedHealth Group. D.Ferrell: Stock/Shareholder; Level2, Medexpress Urgent Care. J.Fung: Employee; Level2.

© 2023 by the American Diabetes Association
2023
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