Background: Glucose transport from blood to interstitial fluid impacts performance of interstitially-placed continuous glucose monitoring (CGM) sensors. We examined time series offsets (“lag times”) of the G7 CGM system (Dexcom) .
Methods: In a pivotal accuracy study conducted in the US, 316 adults with diabetes wearing 6sensors participated in clinic sessions that included glucose manipulations and frequent venous plasma glucose (YSI) determinations. G7 values were obtained every 5 min and interpolated to provide values at 1-min intervals. Each YSI value was associated with 21 G7 values obtained from min before to min after. The absolute relative difference (ARD) was calculated for each YSI:G7 pair and each sensor’s lag was estimated as the time with the lowest mean ARD.
Results: A lag time of 2 minutes provided the lowest mean ARD of 8.6% and the highest %20/20 agreement rate of 94.4%. The Figure shows summary statistics for the distribution of sensor-specific lag times. Lag times of ≤0 min (where interstitial glucose leads blood glucose) were observed for 2 (33.0%) of the sensors.
Conclusions: The distribution of G7 time series offsets suggests that CGM values may most accurately reflect previous or upcoming blood glucose values. This finding is likely due to technological innovations in G7’s hardware and algorithm. The minimal lag time observed should provide users with confidence in using CGM to manage their diabetes.
X.Zhang: Employee; Dexcom, Inc. J.L.Reid: Employee; Dexcom, Inc., GenMark Diagnostics. T.C.Walker: Employee; Dexcom, Inc., Stock/Shareholder; Dexcom, Inc. J.Welsh: Employee; Dexcom, Inc. A.Balo: Employee; Dexcom, Inc.