CGMS

Continuous glucose monitoring systems (CGMs) are medical devices that measure glucose in the interstitial fluid beneath the skin with near-continuous data. They typically include a subcutaneous sensor, a transmitter, and a display device or app that shows current readings, trends, and alerts. CGMs are real-time (rt-CGMs) or intermittently scanned (isCGMs, also called flash monitors).

A sensor is worn under the skin for several days to two weeks. The transmitter sends data to a reader, smartphone, or insulin pump, where readings appear as a current value, trend arrows, and hypo-/hyperglycemia alarms. Many models are factory calibrated, while others require fingerstick calibration.

Accuracy is described by metrics such as MARD (mean absolute relative difference) relative to blood glucose. CGM readings lag interstitial fluid by a few minutes, which can affect accuracy during rapid changes after meals or dosing.

Clinical use and benefits: CGMs aid management for type 1 and type 2 diabetes, increasing time in range and reducing hypoglycemia. They are often used with insulin pumps and can enable automated insulin delivery in some systems.

Limitations and considerations: wearable life, skin irritation or infection risk, alarm fatigue, cost, and variable insurance coverage. Proper insertion, replacement, calibration (if required), and data interpretation are essential.

Regulation and safety: CGMs are regulated medical devices approved by authorities such as the FDA. Ongoing development seeks to improve accuracy during rapid glucose changes, reduce lag, extend sensor life, and enhance integration with pumps and digital health tools.