Continuous glucose monitor (CGM)
Also known as: CGM, continuous glucose monitoring
A continuous glucose monitor (CGM) is a small sensor worn on the skin, usually on the arm or belly, that measures glucose levels in the fluid under the skin every few minutes, day and night.
Readings appear on a phone or receiver, with alarms for highs and lows. While CGMs transformed diabetes care, they're now also sold over the counter to people without diabetes, a market where the health benefits are much less clear.
Continuous glucose monitor (CGM), explained at three levels
At home
People with diabetes used to prick their fingers several times a day to check blood sugar. A CGM is a small patch with a tiny sensor that checks it automatically every few minutes and sends the results to your phone.
At work
CGMs give clinicians a full picture of a patient's glucose patterns, not just a few snapshots, which helps adjust treatment more safely and effectively.
At home
A thin filament under the skin measures glucose in interstitial fluid, not blood directly, so readings lag blood glucose by several minutes. Sensors typically last 10 to 15 days. Apps show trends and arrows indicating whether glucose is rising or falling.
At work
Key metrics include 'time in range' (the percentage of time glucose stays in a target range), glucose variability, and time below range. CGMs connect to insulin pumps in automated delivery systems and share data with clinics through cloud platforms.
At home
For people without diabetes, CGM data can encourage healthier habits, but it can also cause needless worry about normal spikes after meals. In my opinion, wellness CGM marketing often promises more insight than the evidence supports.
At work
Considerations include accuracy (measured by MARD), interoperability standards for connecting with pumps, coverage policies, data privacy as CGM data flows to apps and third parties, and cybersecurity for connected insulin systems. Equity matters: coverage gaps mean many eligible patients still can't afford sensors.
Real-world examples
At home
Lena has had type 1 diabetes since childhood. Switching to a CGM meant her phone alarmed when her blood sugar dropped at night, something finger pricks could never catch. She sleeps far better now.
At work
Marcus is a diabetes educator at an Alberta clinic. Reviewing patients' CGM reports, he sees overnight lows and after-meal spikes that were invisible before, and adjusts plans with patients during shorter, more focused appointments.
How it compares
| feature | Continuous glucose monitor (CGM) | Finger-prick meter |
|---|---|---|
| Frequency | Every few minutes | Only when tested |
| Alerts | Yes, for highs and lows | No |
| Measures | Interstitial fluid glucose | Blood glucose |
| Cost | Higher, ongoing sensors | Lower |
A CGM shows the whole film. A finger-prick shows a single frame.
For analysts
For employers and insurers, CGM coverage can be a cost-saving investment by preventing complications. I'd look at time-in-range outcomes and hospitalization data rather than sensor cost alone.
History & origin
Medtronic received FDA approval for the first professional CGM in 1999, which stored data for doctors to review later. Dexcom launched its first real-time personal CGM in 2006. Abbott's FreeStyle Libre, introduced in Europe in 2014, made 'flash' glucose monitoring affordable and needed no finger-stick calibration. CGMs became the backbone of automated insulin delivery systems, sometimes called artificial pancreas systems. In 2024, the FDA cleared the first over-the-counter CGMs, Dexcom's Stelo and Abbott's Lingo, for adults not using insulin. Canadian provinces have expanded public coverage for CGMs for people with diabetes. In my view, the CGM is one of the clearest examples of wearable technology genuinely changing lives.