Continuous Glucose Monitoring (CGM)
A technology using a small sensor placed under the skin to measure glucose levels continuously throughout the day. CGM provides detailed data on glucose patterns, variability, and time in target range. CGM data are increasingly used as outcome measures in diabetes drug trials.
Technical Context
CGM systems: a subcutaneous sensor (electrochemical glucose oxidase or fluorescence-based) measures interstitial glucose every 1-5 minutes, transmitted wirelessly to a receiver or smartphone app. Sensor duration: 7-14 days depending on system. Accuracy: mean absolute relative difference (MARD) of 8-12% for current devices. CGM-derived metrics beyond TIR/TBR/TAR include: glucose management indicator (GMI — estimated HbA1c from CGM data), area under the curve above/below threshold, episodes of hypoglycaemia/hyperglycaemia (duration and nadir/peak), and ambulatory glucose profile (standardised visualisation). CGM is increasingly used in clinical trials: the FDA accepts TIR as a meaningful endpoint, and CGM data provide richer glycaemic information than HbA1c alone. For GLP-1 RA trials, CGM data demonstrate improvements in TIR and reductions in glycaemic variability alongside HbA1c reduction.