Pathophysiology
Clinical meaning
Modern diabetes technology has transformed glycemic management by addressing the fundamental limitation of traditional fingerstick monitoring — its episodic, retrospective nature. Continuous glucose monitoring (CGM) systems, insulin pump therapy (continuous subcutaneous insulin infusion, CSII), and hybrid closed-loop (HCL) or automated insulin delivery (AID) systems work together to approximate the minute-to-minute glucose regulation of a functioning pancreas. CGM devices measure interstitial fluid glucose via a subcutaneously inserted electrochemical sensor (typically glucose oxidase-based or fluorescence-based). The sensor generates an electrical signal proportional to glucose concentration, sampled every 1–5 minutes and transmitted wirelessly to a receiver, smartphone, or insulin pump. Critical to clinical interpretation is the physiological lag time of 5–15 minutes between blood glucose and interstitial glucose — during rapid glucose changes (post-meal spikes, exercise-induced drops), interstitial glucose lags behind capillary blood glucose. This lag explains why CGM and fingerstick readings may differ, particularly when glucose is changing rapidly. Current-generation CGM sensors (e.g., Dexcom G7, FreeStyle Libre 3, Medtronic Guardian 4) achieve MARD (mean absolute relative difference) of 8–10%, meeting the accuracy threshold for insulin dosing decisions without confirmatory fingersticks. Insulin pump...