Optimal Sampling Duration for Continuous Glucose Monitoring to Determine Long-Term Glycemic Control

Objective: To determine the minimum sample of continuous glucose monitoring (CGM) data needed to accurately reflect 3 months of glycemic control. Research Design and Methods: Three months of CGM data were collected on 257 individuals (age 10-78 years) with type 1 diabetes in two studies (one using the Abbott FreeStyle Libre Pro and the other using the Dexcom G4). Correlations were calculated between the full 3 months and incremental sampling periods of CGM data. Results: Correlation to the full 3 months of data improved with an increasing number of days of data collection, plateauing by about 14 days, with an R-2 value of 0.84-0.86 for mean glucose, time at 70-180mg/dL, and time >180mg/dL, with lower values for time <70mg/dL (0.76) and coefficient of variation (0.70). Conclusions: Fourteen days of CGM data provide a good estimation of glucose metrics for a 3-month period.