What is a Continuous Glucose Monitor?

Reviewed by: HU Medical Review Board | Last reviewed: February 2021.

Continuous glucose monitors (CGM) track blood glucose (blood sugar) automatically, day and night. CGMs let you see your blood glucose levels at any time. If your glucose rises or falls beyond a pre-set level, the CGM can send an alarm.1

These monitors also make it easy to collect your numbers so you can spot trends in how your glucose rises and falls over hours or days. This information can be used to help you fine-tune your food, activity, and medicines to more tightly control your blood sugar levels.

There are 2 types of CGMs: real-time CGM and intermittently scanned CGM (also called flash monitoring). Several models are available for the U.S. market. You need a prescription to get a CGM.1

How do continuous glucose monitors work?

CGMs have several parts that work together to monitor your blood glucose levels, including:1,2

  • Glucose sensor and transmitter. A tiny sensor is inserted under the skin, usually on the belly or arm. A sticky patch keeps the sensor in place. This sensor measures interstitial glucose levels, which is glucose found in the fluid between the cells. Every few minutes, the sensor sends its readings to a monitor through a transmitter.
  • Receiver and display. A CGM receiver collects data sent by the sensor and then displays it on a screen. It is usually small enough to be clipped to the waistband of pants, tucked into a pocket, or placed in a purse or nightstand.

Many CGM brands need to be used with a glucometer (blood glucose meter) to check the accuracy of their readings. This means the person must also stick their finger 2 or more times a day to double-check their blood glucose numbers.1,2

CGMs may be used with an insulin pump. It may also send data directly to a smartphone or tablet. The CGM sensor (the part under the skin) needs to be replaced every few days, depending on the brand. The sticky patch needs to be placed in a different location each time to prevent skin irritation.1,2

Who uses CGMs?

Continuous glucose monitors can be especially helpful for certain groups, including:1,2

  • People with type 1 diabetes
  • People with type 2 diabetes who need to tightly control their insulin therapy
  • People who find it hard to recognize symptoms of low blood sugar (called impaired hypoglycemia awareness)
  • Children and other people who have a hard time remembering to regularly check their blood glucose
  • Athletes who have diabetes
  • People who often have high or low blood glucose
  • People who have nocturnal (nighttime) hypoglycemia (low blood glucose)
  • People with pre-diabetes

A CGM can be used all the time or over a few days when a diabetes care plan needs to be changed.

The benefits of a continuous glucose monitor

There are several benefits to using a CGM along with a standard blood glucose meter (glucometer). CGMs allow for:1,2

  • Tighter blood sugar control, which is known as intensive insulin therapy
  • Less risk of low blood sugar
  • Fewer finger sticks
  • Alerts to be sent to caregivers

Studies have found that people who see the real-time effects of their eating and exercise are more likely to make changes that keep their blood glucose better under control. Tighter glucose control keeps people with diabetes healthier and prevents complications of the disease.3

The drawbacks to a CGM

There are many advantages to using a continuous glucose meter, especially convenience and more detailed information about your blood glucose levels. However, there are some drawbacks to these devices. First, a CGM is more expensive than a standard glucose meter and may not be covered by your insurance. However, a CGM may be less expensive for people who have to stick themselves several times a day with a standard glucometer.1-3

Most CGMs must be double-checked for accuracy at least twice a day. This means that you must use a standard glucose meter before taking action due to a low or high glucose reading on your CGM.1,2

Some brands of CGM sensors last longer than others, creating a “hassle factor” in remembering to change and move the sensor, plus added expense. Finally, the sticky patch used to keep the sensor from moving can irritate some people with sensitive skin.2

The future of CGMs

As more people begin to use CGMs and the technology improves, diabetes educators will be better able to help people use their data to improve their health. Better control of weight, blood pressure, and blood glucose will help people with pre-diabetes or diabetes use less medicine and stay healthier, longer.

Ultimately, doctors would like to create what is called an artificial pancreas system. CGMs would play a role in replacing the activities of the human pancreas with a combination of devices and technology.1

By providing your email address, you are agreeing to our privacy policy.