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A continuous glucose monitor, or CGM, is a wearable device that estimates glucose levels throughout the day and night. Most systems use a small sensor placed under the skin to measure glucose in interstitial fluid. A transmitter or sensor sends readings to a receiver, insulin pump, or smartphone app. CGMs show trends and alerts, but they are not a complete replacement for clinical diabetes care.
read more about continuous glucose monitor ...A continuous glucose monitor is used to help people with diabetes track glucose patterns more often than finger-stick checks alone. It can show whether glucose is rising, falling, or staying stable. CGMs can help guide treatment decisions, detect trends, and alert users to high or low glucose levels. The diabetes care team helps decide how CGM data should be used with medication, food, activity, and insulin dosing.
The sensor measures glucose in the fluid between cells rather than directly from the blood. The device converts sensor signals into estimated glucose readings at regular intervals. Some systems need scanning, while others send readings automatically. Because interstitial glucose can lag behind blood glucose, readings may differ during rapid glucose changes.
A CGM system usually includes a sensor, transmitter or integrated sensor unit, receiver or app, adhesive patch, and insertion device. Some systems connect with insulin pumps or automated insulin delivery systems. Sensors must be replaced on the schedule listed for the device. Alerts, alarms, data sharing, and calibration needs vary by system.
CGM readings can be affected by sensor placement, compression, medication interference, dehydration, rapid glucose shifts, or device problems. Users should follow the device instructions for calibration, alerts, sensor changes, and finger-stick confirmation when symptoms do not match readings. Missed smartphone alerts can create safety risks if the user relies on the app for alarms. Severe low blood sugar, persistent high readings, ketones, confusion, or symptoms that do not match the device should be treated according to the care plan.
Most CGMs measure glucose in interstitial fluid, not directly in blood. This can cause a short delay compared with finger-stick blood glucose.
Some systems reduce routine finger sticks, but finger-stick testing may still be needed when symptoms do not match the reading, during rapid changes, or when the device requests it.
Placement depends on the device labeling. Common sites include the abdomen, upper arm, or other approved body areas.
Yes. Smartphone settings, signal issues, dead batteries, app problems, or alert settings can affect alarms. Users should follow device instructions and keep backup testing supplies.
Continuous Glucose Monitoring. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/diabetes/overview/managing-diabetes/continuous-glucose-monitoring. Date Accessed June 18, 2026.
Continuous Glucose Monitoring (CGM): What It Is. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/continuous-glucose-monitoring-cgm. Date Accessed June 18, 2026.
Continuous Glucose Monitoring (CGM). American Diabetes Association. https://diabetes.org/advocacy/cgm-continuous-glucose-monitors. Date Accessed June 18, 2026.
FDA Clears First Over-the-Counter Continuous Glucose Monitor. U.S. Food and Drug Administration. https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor. Date Accessed June 18, 2026.
Continuous Glucose Monitoring, Mobile Technology, and Insulin Pump Therapy. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK279046/. Date Accessed June 18, 2026.