Accuracy of Continuous Glucose Monitoring in Adults With Postbariatric Hypoglycemia After Roux-en-Y Gastric Bypass Surgery Under Stable and Dynamic Glucose Conditions

OBJECTIVE: Although continuous glucose monitors (CGMs) are increasingly used to detect and manage postbariatric hypoglycemia (PBH) and associated glucose variability, data on their accuracy in this population remain scarce. RESEARCH DESIGN AND METHODS: We retrospectively assessed the accuracy of the Dexcom G6 CGM system in adults with PBH after Roux-en-Y gastric bypass (RYGB) surgery (n = 70). Glucose excursions were induced using a standardized solid mixed-meal test, and reference blood glucose (BG) values were obtained through repeated venous whole-blood sampling. CGM accuracy was analyzed separately during stable and dynamic postmeal glucose periods, with dynamic phases stratified according to magnitude and direction of the rate of change (RoC). We further estimated the lag time for each sensor and examined predictive factors affecting CGM accuracy. RESULTS: A total of 1,822 CGM-BG pairs obtained with 70 individuals were included in the analysis. Mean absolute relative differences at stable and dynamic levels were 9.6% and 16.4%, respectively. After the meal test, 67.6% of pairs had CGM values within 15%, or 15 mg/dL of the reference BG; 78.0% within 20%, or 20 mg/dL; and 90.8% within 30%, or 30 mg/dL. Performance was worse at rapid plasma glucose decline (>1.5 mg/dL/min), and CGM values at the time of plasma glucose nadir were systematically higher (bias, 8.2 mg/dL). Plasma-interstitium time delay was estimated at 9.8 min. No participant or sensor characteristic had a significant impact on CGM accuracy. CONCLUSIONS: Meal-induced glucose dynamics, particularly rapid declines, challenge CGM accuracy in people with PBH and must be carefully considered when diagnosing or managing the condition.