Continuous glucose monitor
 Abbott Laboratories' FreeStyle Libre CGM. The sensor and transmitter are fixed to the upper arm. The receiver shows the blood glucose level and a graph of recent blood glucose levels. | |
| Classification | Medical device |
|---|---|
| Uses | Blood glucose monitoring |
| Related | Fingerprick testing |
A continuous glucose monitoring (CGM) system is a medical or wellness device used to continuously track interstitial glucose levels in real time, replacing the need for periodic finger-stick blood draws. Tracking interstitial glucose is a valid way to monitor blood glucose due to their high correlation, despite a lag time in glucose levels between the interstitial space and the bloodstream.
While historically reserved for clinical diabetes management, such as tracking by individuals with type 1, type 2 or gestational diabetes, CGM systems are widely utilized by non-diabetic populations. These include individuals with metabolic conditions like prediabetes or polycystic ovary syndrome (PCOS), elite athletes optimizing endurance fueling, and health-conscious consumers tracking personalized dietary responses, weight management, and everyday metabolic fitness.
The early generations of these systems typically consisted of a sensor patch (worn on the back of the upper arm or the side of the torso) paired with a separate, portable handheld reader to display results. Modern sensors use Bluetooth to transmit data directly to a smartphone app, allowing users to view trends, receive high or low alerts, and share their metabolic data with healthcare providers or coaches in real time.
Most CGMs are electrochemical systems that utilize an enzymatic reaction with glucose molecules in the body's interstitial fluid. This reaction generates electrical current on the nanoampere (nA) scale that is directly proportional to the localized glucose concentration. The resulting data is then wirelessly transmitted from the patch to a paired device, where the real-time readings are displayed to the user. The FreeStyle Libre 3 by Abbott, AccuCheck Smart Guide by Roche, Dexcom G7 by Dexcom, Guardian 4 by Medtronic, SIBIO by Sibionics are examples of electrochemical CGM systems. These systems are known as minimally invasive, since sensor application requires a physical insertion of the sensing filament in the subcutaneous skin tissue. Operational time of electrochemical CGMs spans 14-16 days.
Some CGMs utilize an optical detection (fluorescence) of glucose to provide a real time reading, e.g., the Eversense 365 by Senseonics. However, the installation of such systems requires a minor surgery, so the device is installed by professionals in the clinic and not by the user. Operational time of optical CGM systems is much higher and can last up to one year.
Some CGM systems must be calibrated once at the activation, or calibrated periodically with traditional blood glucose measurements to establish the baseline for the measurement and compensate for the drift, whereas others do not require calibration by the user (factory calibration).