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.

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. It is constantly reading your blood sugar level. It sends this information to the other part of the monitor, a wireless receiver. 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.

Some CGMs need you 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.

Some CGMs have an alarm feature 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 need to be changed. Depending on the system, you may need to change the sensor every few days. Some systems have sensors that last 10 days.
• Some CGMs will require that you prick your finger to confirm the CGM's accuracy.
• Acetaminophen (Tylenol) can affect the results in some CGMs, reporting the readings higher than they actually are.