Continuous Glucose Monitoring

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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 several 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. Some insulin pumps include CGM. In this case, the insulin pump is also the receiver.

At any time, you can look at the receiver and see what your glucose level is. Some systems use text messages, apps, and websites. You can see if your level is going up or down-and how fast. You can see the trends and patterns of your glucose levels.

You note on the receiver when you eat, do exercise, and take 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 several times a day, depending on the manufacturer's directions, 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.

What are the drawbacks?

  • 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 several times a day to confirm the CGM's accuracy. The number of times a day you need to do a finger prick depends on the CGM you use.
  • Acetaminophen (Tylenol) can affect the results, reporting the readings higher than they actually are. Manufacturers of CGM warn against taking acetaminophen while you are using CGM.

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.

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Other Works Consulted

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


ByHealthwise Staff

Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine

Kathleen Romito, MD - Family Medicine

Adam Husney, MD - Family Medicine

Specialist Medical Reviewer Rhonda O'Brien, MS, RD, CDE - Certified Diabetes Educator

Current as ofDecember 7, 2017