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 R2 value of 0.84-0.86 for mean glucose, time at 70-180 mg/dL, and time >180 mg/dL, with lower values for time <70 mg/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.