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 therapy delivers rapid-acting insulin through a subcutaneous catheter, providing continuous basal infusion (replacing long-acting insulin) with user-initiated boluses for meals and corrections. Pump advantages include programmable basal rate profiles (addressing dawn phenomenon with higher overnight rates), precise dosing in increments as small as 0.025 units, extended bolus options for high-fat meals (dual-wave or square-wave boluses that deliver insulin over hours), and integration with CGM data.