CGM

CGMs use enzymatic electrochemical sensors inserted into subcutaneous tissue, typically on the arm or abdomen. The sensor contains glucose oxidase enzyme immobilized on an electrode surface. When glucose diffuses from interstitial fluid into the sensor, glucose oxidase catalyzes its oxidation, transferring electrons to the electrode and generating a current proportional to glucose concentration. Modern CGMs sample every 1-5 minutes and wirelessly transmit data to smartphones or dedicated receivers. Interstitial glucose lags arterial blood glucose by 5-15 minutes due to diffusion time, which is clinically significant during rapid glucose changes. Factory-calibrated CGMs use sophisticated algorithms trained on paired blood glucose data to eliminate user calibration. Accuracy is expressed as Mean Absolute Relative Difference (MARD)—modern systems achieve 9-11% MARD. CGMs are FDA-regulated Class II medical devices requiring 510(k) clearance for diabetes indications.