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What is a continuous glucose monitor?

A continuous glucose monitor (CGM) can help you track your blood sugar in real-time. So how does a CGM work, and who should use it?

Levels Team
WRITTEN BY
Levels Team
UPDATED: 23 Oct 2023
PUBLISHED: 03 Dec 2021
🕗 5 MIN READ
ARTICLE HIGHLIGHTS
A continuous glucose monitor is a wearable device that provides real-time blood sugar data by inserting a sensor just under the skin that reads glucose levels in the interstitial fluid.
CGM data can show individual food reactions, improve metabolic flexibility to burn fat, and catch insulin resistance early before it progresses to prediabetes or diabetes.
CGMs help people with diabetes better manage their blood sugar, but they also provide valuable insights for anyone into how diet and lifestyle impact glycemic variability and metabolic health.
Easy access to consistent data on blood sugar responses allows people to make informed diet and lifestyle choices to support longevity, mood, energy levels, weight, and disease prevention.
Though still prescription-only in the US, doctors are increasingly prescribing CGMs for general wellness to optimize health and prevent disease.

A continuous glucose monitor (CGM) is a wearable biosensor that can give you real-time information about your blood sugar (glucose) level. This information is vital to people with Type 1 or Type 2 diabetes, for whom high blood sugar levels (hyperglycemia) or low blood sugar levels (hypoglycemia) can be life-threatening. But CGM devices are also valuable for people without metabolic impairment, serving as a window onto how diet and lifestyle decisions affect their health. Consistently high glucose levels or frequent glucose spikes and crashes can lead to short-term health effects like fatigue, brain fog, and depression and are associated with several chronic diseases, including cancer, cognitive decline, stroke, and cardiovascular disease. CGM can help you maintain stable glucose levels before metabolic dysfunction like insulin resistance (prediabetes) sets in and sets the stage for more severe disease.

Here’s a deeper look at this biosensing technology.

What is a Continuous Glucose Monitor?

A continuous glucose monitor is a plastic disc (about the size of two quarters stacked together) that sticks to the skin, typically on the stomach or upper arm. It sends glucose data continuously (at least every 5 minutes) to a smartphone or handheld device, where the user can see it on a graph or chart. People who have Type 1 diabetes sometimes have their CGM connected to an insulin pump that can automatically deliver insulin if their blood sugar gets too high. Most CGMs last anywhere from 7-14 days before they need to be removed and replaced.

There are three primary manufacturers of CGMs in the US: Abbott, which makes the FreeStyle Libre monitor; Dexcom, which makes the Dexcom G6; and Medtronic, which makes the Guardian system.

Coating the filament is an enzyme called glucose oxidase, which converts glucose to hydrogen peroxide. The hydrogen peroxide reacts with platinum to break down into hydrogen, oxygen, and electrons, which generate current. The device wirelessly transmits this signal to a handheld reader or smartphone, which uses an algorithm to convert the electrical signal to a glucose reading. CGMs have a lifespan of 7-14 days because eventually the chemistry on the sensor degrades, and the reading becomes less accurate.

Future glucose monitoring devices will likely be smaller and last longer, and may measure additional metabolites. They may also incorporate new sensing technology that uses aptamers, or strands of DNA, RNA or amino acids that bind to specific molecules. Aptamers can sense much smaller quantities of a biomarker than current enzymatic sensors.

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Why Use a Continuous Glucose Monitor?

One of the benefits of CGM is that it provides a more granular, real-time look at your blood glucose levels than alternative methods such as using a glucometer, which reads glucose from a drop of blood, or glucose tests at your doctor, such as fasting plasma glucose or HbA1c. These other methods provide only a single measurement, a snapshot in time.

This can fail to show you how much your blood sugar is spiking and crashing (known as glycemic variability [more on that below]). They also fail to reveal glucose trends over time or reactions to particular foods. Even if you tested your blood with a blood glucose meter after a meal, you can’t see the entire rise and fall pattern, so your reading may be misleading. A continuous glucose monitor is like listening to the whole symphony instead of just individual notes.

Who Should Use a Continuous Glucose Monitor?

People with Type 1 diabetes can’t make insulin to help maintain stable blood sugar, so they need to monitor their glucose levels closely to prevent dangerously high or low blood glucose. Without a CGM, the only way to do that is to use a finger-prick glucometer dozens of times a day.

But CGMs can also provide several valuable insights that can benefit people with or without diabetes:

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How Do You Get a Continuous Glucose Monitor?

The FDA has classified CGMs as Class II medical devices, and a healthcare provider must prescribe them. As of 2017, the American Diabetes Association recommends CGMs for people with Type 1 or Type 2 diabetes who need to monitor their blood sugar, although people with Type 1 diabetes still make up the vast majority people who use CGM. Unfortunately, many people with diabetes still struggle to get CGMs approved and covered by their health insurance.

In addition, healthcare professionals are increasingly prescribing CGMs to people without diabetes to help provide them feedback to optimize their health. (So-called “off-label prescriptions” like this make up about 20% of all prescriptions written in the US each year.) In Europe and Canada, CGMs are available over the counter.

Conclusion

Continuous glucose monitoring can improve the quality of life for any individual, whether they have diabetes or not. Access to consistent and accurate data about our blood sugar can help us make informed and healthy diet and lifestyle choices to help support our longevity and wellbeing.

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