The Optimal Duration of a Run-In Period to Initiate Continuous Glucose Monitoring for a Randomized Trial.

To determine the optimal duration of a run-in period for initiation of real-time continuous glucose monitoring (CGM) before the start of a randomized controlled trial (RCT) in type 1 diabetes (T1D) or type 2 diabetes (T2D). Data sets were pooled from 8 RCTs, which had a blinded CGM wear period followed by at least 3 months of unblinded CGM use. Across all participants, mean time in range 70-180 mg/dL (TIR) and mean time <54 mg/dL ( < 54) as well as other key CGM metrics were computed for the initial period of blinded CGM wear and from the subsequent 13 weeks of unblinded CGM use. The analysis cohort included data from 485 participants: 348 with T1D and 137 with T2D, ranging in age from 2 to 82 years. Mean TIR was 49% with blinded CGM before initiation of unblinded CGM use, increased to 55% by the end of the first week of unblinded CGM use, and then showed little change through 13 weeks. Mean  < 54 decreased from 1.4% with blinded CGM to 0.8% 1 week and 0.6% 2 weeks after initiating unblinded CGM use, which matched the value in month 3. Similar results were obtained for mean glucose, time >180 mg/dL, time >250 mg/dL, and time <70 mg/dL, with the mean improvement in hyperglycemia metrics plateauing slightly faster than hypoglycemia metrics. Findings were largely similar for T1D and T2D. When initiating unblinded real-time CGM, improvement in key CGM metrics occurs rapidly, with maximal effect on the mean of each metric achieved within 1-2 weeks. For a randomized trial in which all participants will use real-time unblinded CGM for glucose monitoring, a run-in period should be implemented before collecting baseline data for participants who are not CGM users. For such CGM-naive individuals, a 7- to 14-day acclimation period is sufficient followed by a 14-day period for collection of baseline unblinded CGM data.