What is a Continuous Glucose Monitor (CGM)?

Written by Ally Streelman

NowRx Pharmacy

continuous glucose monitor app for diabetes

A Continuous Glucose Monitor, or CGM, is a wearable device that can help track glucose (blood sugar) levels. How does a glucose monitor work, and who should use one?

Continuous glucose monitoring has been a hallmark of the diabetes community as it enables those with Type I or Type II Diabetes to track their blood sugar continuously. In this way, a continuous glucose monitor can be a life-saving device. 

But today, CGMs are being used by Americans with and without diabetes to track blood sugar—a practice that can help prevent various diseases and health effects. These devices are relatively new. The FDA first approved a CGM for professional use in 1999 and first approved a personal CGM in 2018. New and improved systems for continuous glucose monitoring are coming out every year, so let’s explore how this technology works, how it might benefit you, and what the best glucose monitor devices are.

How does a continuous glucose monitor work?

A continuous glucose monitor works by inserting a small sensor into the upper arm or abdomen. Depending on the glucose monitoring device, the sensor is inserted surgically or simply by attaching a patch. Once inserted, the sensor can read glucose levels in the interstitial fluid. Interstitial fluid is the fluid that sits between the skin and blood vessels. Glucose seeps from the blood vessels into this fluid, which is how a continuous glucose monitor works to deliver a reading of blood glucose levels. 

The beauty of a wearable glucose monitor is that it can track blood sugar in real time. It can then send that data to a device or smartphone app that the user can view. For those with diabetes, a CGM can sometimes connect to an insulin pump that can read the data and deliver insulin when blood sugar levels are too high. 

What is Glucose?

Let’s back up. What is glucose, and why is it important to track? Glucose is a molecule that our bodies need to function—it’s our primary source of energy. We get glucose mainly through the foods we eat. However, the body can also create glucose.

Glucose is often referred to as blood sugar. Chemically, glucose is sugar, but not quite like the sugar you use to bake—that sugar is a combination of glucose and fructose. It’s called blood sugar because it travels throughout the body via the blood to reach the muscles. The muscles can then use glucose as energy.  

Glucose levels affect our mind and body in both the short and long term. In the short term, high blood sugar can send us on a “sugar high,” while low blood sugar can leave us feeling lethargic. In the long term, high blood sugar can have a more dramatic effect on our health. It can eventually lead to diabetes and other chronic diseases.

glucose and insulin relationship infographic explaining how glucose is absorbed in the blood

Why is continuous glucose monitoring important?

Continuous glucose monitoring is vital for those who have diabetes and need to supplement their body with insulin to maintain stable glucose levels.

In this situation, monitoring glucose levels with a CGM can help notify those with diabetes when their blood sugar is too high or too low. This can help them avoid potentially life-threatening situations.

Continuous glucose monitoring can also help prevent diseases associated with high blood glucose levels, including heart disease, stroke, some cancers, and depression.

Who should use a CGM?

Anyone can benefit from using a CGM, but it is particularly useful for those with diabetes. 

Monitoring blood sugar levels for individuals with Type I or Type II diabetes can be a matter of life or death. And wearing a CGM can make monitoring blood sugar easier. Additionally, CGMs can help decrease HbA1c (average blood glucose levels) and reduce hypoglycemia. 

Given the extensive research on how elevated blood sugar can lead to long-term health consequences though, even those without diabetes may want to consider using a CGM. Wearing a glucose monitor patch is a simple way to track how everyday lifestyle choices affect blood sugar.  

By monitoring how these choices affect glucose levels throughout the day, it’s possible to make better ones and regulate blood sugar. This can help prevent chronic disease and lower blood pressure and chances of depression.

How to check your blood sugar with a glucose monitor

Checking your blood sugar with a CGM is as simple as learning how to use an app on your phone. In fact, a user-friendly application is how most glucose monitors send the data they track to the wearer. Other CGMs use a physical monitor that displays blood glucose data. Unlike learning how to use a glucometer that relies on consistent finger pricks, a CGM is straightforward and relatively painless. Although, some of the current systems require a finger prick for calibration. 

Start by placing the adhesive patch on your upper arm or abdomen per the instructions. Download the app to your phone and connect it to your device. Now, you’re ready to use your blood sugar tracker. 

Whether you’re using an app or a monitor, you can set alerts to notify you if your blood sugar level is rising too high or falling too low. You can also check the app or monitor throughout the day to see your levels. Typically, the data will be displayed in a graph format, which will clue you in to how high or low your blood sugar goes over a specific time period.

When to check your blood sugar

At the start, you should check your blood sugar at regular intervals throughout the day to understand your data. As you learn your patterns, you can check the data as much or as little as you wish.

The benefit of a continuous glucose monitor is that it’s continuous, meaning you can read your glucose levels throughout the day and see how food and exercise affect those levels in real time (typically, with a 5-minute delay). Different foods and exercise do affect your blood glucose levels differently. Some have a spiking effect, while others have a regulating effect. There are overarching trends, i.e., carbohydrates will spike blood sugar more than protein, but the specific effects are different for everyone. By checking your blood sugar before and after meals, you can learn how certain foods and meals affect it.

As you learn which foods result in higher blood sugar levels or spikes and crashes, you can alter your choices accordingly.

What is the best glucose monitor?

The best glucose monitor depends on your personal preferences. Here are a few popular options for continuous glucose monitoring. 


The Dexcom glucose monitor, called the Dexcom G6 CGM System, is well known for its accuracy and customizable settings. Settings include alarms and alerts when blood sugar levels are too high or too low. The device is water-resistant and easy to apply at home. It lasts up to 10 days and delivers data ​​via a small touch screen receiver or a compatible smart device like a phone or watch. 


Like the Dexcom G6, the Freestyle Libre 2 from Abbot is an easy-to-apply patch CGM. It also delivers alarms that signal dangerous glucose levels and provides data through a reader or app. It’s wearable for up to 14 days and is suitable for adults and children four and up. 


The newest FDA-approved CGM, which will be available in the spring of 2022, is the Eversense E3 System. It is also the longest-lasting CGM approved in the world, lasting six months. 

How long a CGM lasts refers to how long its sensor lasts. Depending on the brand, CGM sensors need to be replaced anywhere from every few weeks to every few months. At six months, the longevity of the Eversense E3 sensor is the longest yet. Unlike the systems above, the Eversense E3 system relies on a fully implanted sensor, which requires a procedure to be implanted, removed, and replaced.


For those who want to track their blood sugar from their phone and wear an inconspicuous glucose monitor patch 24/7, Levels is a good option. While the other systems on this list focus on serving those with diabetes, Levels is available (via a prescription) to anyone looking to monitor their glucose levels for enhanced health. 

How to get a continuous glucose monitor

In the U.S., you need a prescription from your doctor to get a CGM. This is because CGMs are medical devices. Many doctors will prescribe CGMs to patients with Type I or Type II diabetes, but they may also prescribe them to patients looking to track their blood sugar to optimize health and prevent disease. 

If you’re interested in using a continuous glucose monitor to track your blood sugar, talk to your physician and discuss the benefits of integrating this system into your treatment or prevention plan.

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