What is a CGM? 

A continuous glucose monitor (CGM) tracks glucose levels in real-time for people with diabetes. 

Unlike traditional fingerstick methods, a CGM provides continuous readings using a small sensor inserted under the skin. This sensor measures glucose levels, transmitting data to a monitor or smartphone app, allowing users to see trends and fluctuations in their glucose levels throughout the day. This continuous feedback helps users make informed decisions about food, exercise, and medication!

We can send you the latest and greatest information on diabetes straight to your inbox once a month—for free! Sign up today and then scroll down to get your answers about diabetes technology answered—including CGM basics, different kinds of CGMs available, and more. 

How can a CGM help you?

Continuous glucose monitors have changed the game for people with diabetes.

There are over 42 factors that can affect your blood sugar—a CGM helps you manage them. A CGM measures your glucose (sugar) levels in real-time and lets you see what your blood sugar at every moment of the day. They work by sensing the glucose present in tissue fluid (also called interstitial fluid), and send those readings straight to your phone! When you wear a CGM, you don’t have to rely on finger-sticking anymore—and you have more knowledge about where your glucose has gone, and where it might go. 

Unlike blood glucose meters (BGMs) where you have to prick yourself, CGMs typically provide a new glucose level reading every minute or five minutes One could liken a BGM to a photo – providing a single blood sugar “snapshot” – while a CGM is like a video, providing a constant stream of information on glucose levels, trends, and overnight data. 

CGMs are particularly useful after meals and overnight, as they can sound an alert when your blood sugar is high or low. They can even tell you before your sugars rise and fall so you can take action to prevent feeling bad.

Privacy Terms

Who can use CGM?

People with any kind of diabetes can benefit from diabetes technology like continuous glucose monitors (CGM), even if you aren't taking insulin!

A CGM can tell you where your glucose levels are every single minute of the day, so you can see the whole picture of your glucose. Using CGM metrics can help you identify patterns that show you how different foods, exercise, feelings, and more affect your glucose levels, which allows you to make changes based on those patterns.

Using a CGM and its metrics have been shown to help decrease long-term diabetes complications, lower A1C, improve quality of life, and so much more. This is important for people with Type 1 diabetes, Type 2 diabetes, LADA, and more.

What CGMs are available?

Depending on your insurance coverage, different CGMs will be available to you. If you have private insurance, you can use this tool  to see what CGMs are covered by your insurance. If you are on Medicare and you have Type 2 diabetes and take insulin or have had severe hypoglycemia, CGMs should be covered for you. You can learn more about coverage here. 

In 2024, over-the-counter CGMs will be available to people with Type 2 diabetes who are not on insulin! This includes Abbot's Rio and Dexcom Stelo. Speak to your pharmacy about when they will be available in your area. 

Robert Greene

Living with Type 2 diabetes

There are 42 factors that affect glucose levels—you should have the freedom to know exactly how they affect you. You can learn more about how to get started with a CGM, including answers to questions about insurance and more, at timeinrange.org. 

Linxi Mytkolli

Living with Type 1 diabetes

What can a CGM show you?

One of the most important metrics your CGM can show you is time in range. Ultimately, time in range shows you the ENTIRE picture. 

Time in range (TIR) is the percentage of time that a person spends with their blood glucose levels in a target range. When we refer to TIR, we also mean the metrics that are measured along side it—like time below range (TBR) and time above range (TAR).

Using time in range to manage your diabetes can help you recognize patterns and learn what works best for your body and your life — like how your glucose responds to changes in your food, exercise, sleep, hormones, and so much more. 

Time in range

Using time in range alongside A1C can empower you to learn your glucose patterns in between appointments with your care team, and can facilitate more informed decision-making with your doctor. There are over 42 factors that can cause blood sugar to levels to increase and decrease, and using time in range can help you identify those factors and make changes. You can see what foods raise your blood sugar, what can help you lower blood sugar, and so much more.
 

Maybe your A1C is on target, but you’re really struggling with post-meal highs and re-bound lows—time in range can help you and your care team adjust your management to help you feel better, faster.

If you’re interested in learning more about time in range and how you can get started, sign up for our free monthly newsletter here!

Glucose Management Indicator (GMI)

Glucose management indicator (GMI) provides an estimated A1C level based on your CGM data. Like A1C, the GMI can help you monitor changes in your average glucose levels, but does not provide information on variability—it can't capture the highs and lows, only an average.

Your GMI may be different than your A1C—these differences can be due to recent changes in your management that impact GMI faster than A1C, or due to several factors that impact red blood cells and therefore can affect the reliability of A1C.

It’s very common for your A1C and GMI to be different. A 2021 study looked at how GMI compares to actual A1C and found that 50% of people had differences of at least 0.5 percentage points. GMI is a helpful tool to predict your A1C, but it's not the exact same thing!

Ambulatory Glucose Profile

The Ambulatory Glucose Profile report (or AGP) gives you a snapshot of all your CGM metrics so that you can view your data, what it means, and take action! An AGP report is a standardized, single-page report that includes your time in, above, and below range, your average glucose and corresponding GMI, and your coefficient of variation, which indicates how variable your glucose levels have been. You can find this through your CGM's app.

You may notice the report lists goals next to each number—these are recommendations for most people, but remember that your specific goals are set by you and your care team!

Once you are familiar with your AGP report, you can think about how your routine fits with the patterns you see. Are you usually low in the mornings, when you work out? Do you have a pattern of big spikes late on Friday nights, after your pizza night tradition with friends? Putting these pieces together can help you and your care team adjust your medication and management skills to work better with the things you love to do.