CGM

CGM is short for Continuous Glucose Monitoring, meaning the ongoing tracking of blood sugar levels in the body. A coin-sized sensor is stuck to the upper arm or abdomen. A hair-thin filament reaches a few millimeters under the skin and measures how much glucose is present in the tissue fluid there. Every one to five minutes, the sensor sends a new reading via wireless signal to a smartphone, a smartwatch, or a small reader device. In the past, people with diabetes had to prick their fingers several times a day and place a drop of blood on a test strip. A CGM replaces these individual measurements with a continuous curve.

From a Single Value to a Curve

The crucial difference is not accuracy, but direction. A finger-prick measurement only tells you: right now, the value was this high. Whether it is rising or falling remains unknown. A CGM also shows a trend arrow. Anyone who sees that their blood sugar is dropping sharply can eat something in time before a dangerous low occurs.

Diabetes affects several hundred million people worldwide. Values that are too high over years damage the eyes, kidneys, and nerves, while values that are too low can lead to unconsciousness within minutes. Studies show that CGM users spend significantly more time within the healthy target range. This metric is called Time in Range and has partly replaced the long-term value that was previously the standard measurement.

For investors and tech enthusiasts, CGM is also one of the largest markets in medical technology. Manufacturers like Dexcom, Abbott, and Medtronic don’t make their money from the device itself, but from the sensors, which have to be replaced every one to two weeks. This subscription-like business model explains why this sector is watched so closely on the stock market.

What the Filament Under the Skin Measures

The sensor doesn’t measure sugar directly in the blood, but in the fluid between the cells. The filament carries an enzyme that reacts with glucose. This reaction produces a tiny electrical current. The more sugar present, the stronger the current. A chip in the sensor converts this current into a glucose reading.

This results in a typical quirk: the tissue fluid lags behind the blood by about five to fifteen minutes. So after a sugary drink, the sensor shows the rise with a delay. Modern devices partially compensate for this lag using software. This is precisely where artificial intelligence is increasingly coming into play.

Algorithms learn from the data patterns of many users how a curve is likely to develop further. They warn before a critical value is even reached. In so-called closed-loop systems, this goes even further: the sensor reports its readings to an insulin pump, a program calculates the appropriate dose, and the pump delivers it automatically. This is referred to as an artificial pancreas.

From the Hospital to the Drugstore

Most commonly, CGM sensors are seen as white or gray patches on the upper arm. In children and adolescents with type 1 diabetes, they have now become standard in Germany and are paid for by health insurance. Parents can monitor their children’s readings remotely on their own phone.

Since 2024, the first CGM systems have been approved in the US without a prescription, intended for people without diabetes. They are marketed as a tool for nutrition and exercise. Professional medical societies are cautious here: in healthy people, glucose levels fluctuate anyway, and individual spikes say little about overall health. The benefit for this group is scientifically disputed.

In business news, CGM usually comes up in connection with quarterly earnings, patent disputes, or regulatory approvals. A related term is wearable, meaning body-worn technology such as fitness watches. The difference: a CGM is an approved medical device with strict accuracy requirements, while a fitness watch is not.