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Continuous Glucose Monitoring

Topic Overview

When you test your blood sugar, you learn your blood sugar level at that time. But you can't tell what's happening to your blood sugar the rest of the time—especially overnight. A continuous glucose monitor, or CGM, can do that for you. It reports on your blood sugar at least every 5 minutes, day and night. And it sounds an alarm if it sees that your levels are headed out of range.

How does a continuous glucose monitor work?

A CGM has three parts. You wear one part—the sensor—against your skin. It has a tiny needle that stays under your skin. A transmitter is attached to the sensor and constantly reads your blood glucose level. It sends this information to the other part of the monitor, a wireless receiver that you (or a caregiver such as a parent) wear on your belt or in your pocket.

At any time, you can look at the receiver and see what your glucose level is. You can see if your level is going up or down—and how fast. You can download the information to your computer and see the trends and patterns of your glucose levels.

You note on the receiver when you eat, do exercise, and inject insulin. That way you can see how those activities affect your blood sugar throughout the day and night.

All this detailed information gives you and your doctor a better idea of what your treatment needs are.

Continuous monitors are not as accurate as standard meters. At least once or twice a day, depending on the type of monitor you buy, you will have to prick your finger and use your standard meter to confirm what the CGM is telling you.

What are the benefits?

A CGM is constantly measuring your blood sugar. This information helps some people who have diabetes make decisions about what to eat, how to exercise, and how much medicine to take. Using a CGM has been shown to give people with type 1 diabetes better control of their blood sugar levels, with fewer low blood sugar emergencies.

The alarm feature of a CGM can be set to alert you if your blood sugar is quickly going up or down, or if you have a blood sugar level out of your target range. This is helpful for people who have problems knowing when they have low blood sugar (hypoglycemic unawareness). Parents, partners, or caregivers can be alerted when your blood sugar is dropping quickly while you are asleep.

CGMs also work with some glucose meters and some work with insulin pumps.

What are the drawbacks?

  • A continuous glucose monitoring system can be expensive, and your insurance may not cover the cost. If your insurance does cover the cost, you may have to do some work to get the coverage. You may have to submit records showing how often you took blood sugar readings over a period of time, perhaps a month, and what those readings were. Ask your insurer ahead of time what is covered and what you will need to do to get that coverage.
  • Sensors last just a few days. You must insert a new one every 3 to 7 days, depending on the type.
  • CGMs don't replace finger pricks. You'll still need to prick your finger at least once or twice a day to confirm the CGM's accuracy.

Who is most likely to be successful using this device?

You're most likely to be successful with a CGM if:

  • You are committed to keeping your blood sugar under control.
  • You're willing to learn how to use the CGM.
  • You realize that finger pricks and continuing to use your standard glucose meter are still very important.
  • The idea of having the sensor attached to your body throughout the day and night doesn't bother you.
  • You see well enough to read the monitor and you hear well enough to hear the alarms.


Other Works Consulted

  • Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group (2009). The effect of continuous glucose monitoring in well-controlled type 1 diabetes. Diabetes Care, 32(8): 1378–1383.
  • Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group (2008). Continuous glucose monitoring and intensive treatment of type 1 diabetes. JAMA, 359: 1–13.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Current as of June 4, 2014

