How CGMs Work

Continuous Glucose Monitors (CGMs) measure glucose in the interstitial fluid (ISF) rather than the blood, creating an inherent lag time of 5–20 minutes.

CGM sensor technology relies on amperometric electrochemical detection using Glucose Oxidase (GOx) to convert interstitial glucose into an electrical signal.

CGMs measure interstitial fluid rather than capillary blood, resulting in a physiological lag time of 5–15 minutes that creates discrepancies during rapid glucose changes.

Mean Absolute Relative Difference (MARD) is the gold-standard metric for CGM accuracy, with <10% being the threshold for non-adjunctive use.

The Foreign Body Response (FBR) is the primary physiological limiter of CGM lifespan and accuracy, causing sensors to be walled off by fibrous tissue over time.

CGM accuracy is challenged by three primary noise sources: electrochemical interference, mechanical artifacts, and biological noise from the body's immune response.

Non-invasive glucose monitoring seeks to measure blood glucose without skin penetration using technologies like NIR spectroscopy and RF dielectric sensing.

Modern CGMs use sophisticated calibration algorithms, with many now featuring factory-calibration that eliminates the need for user fingerstick calibrations.

Two key enzymes power CGM sensors: Glucose Oxidase (GOx) offers superior specificity while Glucose Dehydrogenase (GDH) provides different performance characteristics.

CGM technologies include enzymatic sensing (traditional) and fluorescence sensing, each with distinct advantages for glucose detection.

Error grids evaluate CGM clinical accuracy by plotting sensor readings against reference values and categorizing deviations by clinical risk level.

The FDA's iCGM classification establishes interoperability standards allowing CGMs to be used with automated insulin delivery systems.