Within-Person and Between-Sensor Variability in Continuous Glucose Monitoring Metrics

Abstract

Background: The within-person and between-sensor variability of metrics from different interstitial continuous glucose monitoring (CGM) sensors in adults with type 2 diabetes not taking insulin is unclear.

Methods: Secondary analysis of data from 172 participants from the Hyperglycemic Profiles in Obstructive Sleep Apnea randomized clinical trial. Participants simultaneously wore Dexcom G4 and Abbott Libre Pro CGM sensors for up to 2 weeks at baseline and again at the 3-month follow-up visit.

Results: At baseline (up to 2 weeks of CGM), mean glucose for both the Abbott and Dexcom sensors was approximately 150 mg/dL (8.3 mmol/L) and time in range (70180 mg/dL [3.910.0 mmol/L]) was just below 80. When comparing the same sensor at 2 different time points (two 2-week periods, 3 months apart), the within-person coefficient of variation (CVw) in mean glucose was 17.4 (Abbott) and 14.2 (Dexcom). CVw for percent time in range: 20.1 (Abbott) and 18.6 (Dexcom). At baseline, the Pearson correlation of mean glucose from the 2 sensors worn simultaneously was r 0.86, root mean squared error (RMSE), 13 mg/dL (0.7 mmol/L); for time in range, r 0.88, RMSE, 8 percentage points.

Conclusions: Substantial variation was observed within sensors over time and across 2 different sensors worn simultaneously on the same individuals. Clinicians should be aware of this variability when using CGM technology to make clinical decisions.ClinicalTrials.gov Identifier: NCT02454153.

Keywords: continuous glucose monitoring; method comparison; type 2 diabetes; within-person variability.

Figure 1.. Scatterplots and Bland Altman Plots of the within-person variability in CGM mean glucose (comparison of two, 2-week wear periods, 3-months apart), Abbott Libre Pro and Dexcom G4 Platinum sensors, N=153

Two weeks of data at baseline (mean wear time, 12.4 days, SD, 3.0 days) is compared to two weeks of data at follow-up (mean wear time, 12.3 days, SD, 3.1 days). Mean glucose from the Dexcom sensor was calculated, on average, from 3572 readings (every 5 minutes) at baseline and 3542 readings (every 5 minutes) at follow-up. Mean glucose from the Abbott sensor at baseline was calculated from 1190 readings (every 15 minutes) at baseline and from 1181 readings (every 15 minutes) at follow-up. In the scatterplots, the errors-in-variables regression line (dotted blue) and line of identity (solid blue) are shown. Panel A (Abbott), errors-in-variables regression line: Mean glucose, mg/dl (at 3-months) = 1.304 x Mean glucose, mg/dl (at baseline) – 36.012. Bland-Altman: Mean (SD) of difference in mean glucose: 10.1 (36.8) mg/dl. Panel B (Dexcom), errors-in-variables regression line: Mean glucose, mg/dl (at 3-months) = 1.263 x Mean glucose, mg/dl (at baseline) – 31.712. Bland-Altman: Mean (SD) of difference in mean glucose: 8.7 (31.4) mg/dl.

Figure 2.. Scatterplots and Bland Altman plots of mean glucose and percent time-in-range (glucose 70-180 mg/dL) from two CGM devices worn simultaneously (~2 weeks), N=172

Two weeks of data (mean wear time, 12.4 days, SD, 3.0 days). Mean glucose and % time in range (70-180 mg/dL) from the Dexcom sensor was calculated, on average, from ~3572 readings (every 5 minutes). Mean glucose and % time-in-range (70-180 mg/dL) from the Abbott sensor was calculated, on average, from ~1190 readings (every 15 minutes). Errors-in-variables regression line (dotted blue) and line of identity (solid blue) are shown. (A) Errors-in-variables regression: Mean glucose (Dexcom), mg/dl = 0.904 x [Mean glucose (Abbott), mg/dl] +16.906 (B) Bland-Altman: Mean (SD) of difference in mean glucose (Abbott minus Dexcom) = −2.4 (20.0) mg/dl (C) Errors-in-variables regression: % Time-in-range (Dexcom), % = 0.993 x [% Time-in-range (Abbott), %] + 1.981 (D) Bland-Altman: Mean (SD) of difference in % Time-in-range (Abbott minus Dexcom)= −1.4 (11.2) %