Continuous Glucose Monitoring

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Continuous Glucose Monitoring

Topic Overview

As someone with diabetes, you know that if your pancreas were working as it should, it would always know when your blood sugar was going up or down. And then it would provide just the right amount of insulin to keep your blood sugar where it needs to be.

Instead, you have to do that job yourself. You prick your finger and place a bit of blood into your glucose meter. Then you give yourself insulin based on what the meter says your glucose level is (or you tell your insulin pump to do it for you). The more often you test your blood sugar during the day, the better you can see how your meals and activity are affecting your levels, and the better you can control your blood sugar.

But even if you are pricking your finger 15 times a day, 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 two parts. You wear one part—the sensor—against your skin. It has a tiny needle that stays under your skin and constantly reads your blood glucose level. It sends this information to the other part of the monitor, a wireless receiver that you 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.

How well does it work?

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.

  • One study compared adults who used CGMs for 6 months to adults who used only standard meters. The study found that those who used CGMs:1
    • Were more likely to lower their A1c levels.
    • Were more likely to get their A1c below 7% (the recommended level for adults is 7% or less).
    • Had fewer low blood sugar emergencies.
    • Spent more time every day within their target glucose range.
  • Another study showed that even people who already have good blood sugar control can benefit from CGMs. The study found that those who used CGMs were able to keep good blood sugar control with fewer low blood sugar emergencies than those who relied on standard glucose meters.2

What are the drawbacks?

  • A continuous glucose monitoring system is 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. It is a complicated piece of equipment and takes some time to understand and use.
  • You realize that finger pricks and continuing to use your standard glucose meter are still very important.
  • The idea of having the monitor 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.



  1. Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group (2008). Continuous glucose monitoring and intensive treatment of type 1 diabetes. JAMA, 359: 1–13.
  2. 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.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer Matthew I. Kim, MD - Endocrinology
Specialist Medical Reviewer David C.W. Lau, MD, PhD, FRCPC - Endocrinology
Last Revised May 9, 2011

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