Continuous glucose monitoring, also called CGM, is a new way for people with diabetes to monitor glucose levels. CGM measures glucose levels in the fluid between body cells every few minutes throughout the day and night. Most people who use CGM have type 1 diabetes, and many also use an insulin pump.
The most common way to check blood glucose levels is to prick a finger to get a drop of blood (called a fingerstick) and then to test the blood with a blood glucose meter. People use the results of blood glucose tests to make decisions about food, medicines, and exercise.
CGM has a number of advantages over fingerstick testing. In addition, a CGM system sounds an alarm when glucose levels are too high or too low. Users can set the alarm to fit their personal glucose targets.
Although CGM is not as accurate as fingerstick testing, it can provide much more information about blood glucose levels.
A CGM system consists of three main parts:
To make CGM readings more accurate, users enter the results of fingerstick blood glucose tests into the monitor about twice a day. This process (called calibration) is like setting a watch to match the correct time on a clock.
CGM systems provide several kinds of reports about glucose levels. For example, one report graphs average glucose levels for several hours or a whole day and night. CGM systems also allow users to note when they ate meals or took medicines, which can help them understand their glucose trends.
Fingersticks only show glucose levels at certain points in time. Fingerstick testing is like seeing photos of glucose levels to get a sense of what happened that day. In contrast, CGM shows the ups and downs of glucose levels around the clock. It’s like watching a movie of glucose levels. Information about glucose trends helps users take steps to keep blood glucose levels in a safe range. Users can share reports from the CGM system with their health care team to guide any adjustments to their diabetes management plan. (On-the-spot insulin adjustments still need to be based on fingerstick testing.)
Studies have shown that CGM can help people with type 1 diabetes keep blood glucose levels on target without an increased risk for episodes of severe low blood glucose (hypoglycemia). Staying on target can mean fewer health problems, day-to-day and in the long run.
Some people may decide that CGM is not for them. They find it hard to get used to having a sensor under the skin and dealing with alarms. Some may be overwhelmed by the amount of information CGM provides. Also, CGM is not as accurate as fingerstick testing, since glucose measures in the body fluid lag behind glucose measures in the blood. This difference can be an issue in detecting hypoglycemia or when glucose is fluctuating, such as after meals. CGM users should still confirm any results with a fingerstick before taking steps to correct high or low glucose levels.
CGM systems can be costly. A starter kit can be $1,000 or more, and the disposable sensors run about $10 to $15 per day. Health insurance may or may not pay for CGM.
It’s best to talk it over with your doctor. If your doctor recommends CGM, you may be able to try out a system before buying one.