What Is a Continuous Glucose Monitor (CGM)?

A certified diabetes educator and member of the OTD advisory board tells you what you need to know about using a continuous glucose monitor, also called a CGM.

What is a CGM?

A continuous glucose monitor (also called CGM or sensor) is a diabetes device that is inserted and worn under the skin for a specified number of days that can read and record glucose readings every few minutes. A CGM can be worn by people with both type 1 and type 2 diabetes.

Due to the constant, real-time blood glucose monitoring enabled by a CGM, many people with diabetes report better glucose control which often goes hand-in-hand with an improved quality of life. 

Components of the CGM
There are 3 basic parts of a continuous glucose monitor: 

The sensor. This is a disposable piece—usually a very small wire that is inserted under the skin. The sensor reads the glucose in the fluid under the skin and gives a reading. Wear times vary depending on the manufacturing company. Typically, 7-14 day wear.

The transmitter. This reusable piece captures the sensor readings and sends them to another device for the wearer to see it. It works via radio frequency or is Bluetooth enabled.

The receiver. This is the device that communicates with the transmitter to display the glucose readings from the sensor.

Basic Information of how a CGM worksThe basic components of a continuous glucose monitor (CGM) and how they work.

Today's CGMs: Many Variations  

There are 5 different type of CGMs on the market today—not every version is designed to be integrated with an insulin pump. Some people with diabetes monitor their blood sugars using a CGM, finger pricks and insulin shots. Medtronic, Tandem, Animas, Dexcom and Abbott all make personal CGMs for home use. Learn more by visiting their websites, listed below.

For training purposes, doctors offices or diabetes care centers have access to CGMs specially designed for healthcare professionals. These CGMs are used over a short period (7-14 days) to collect data and to allow patients to sample various models. Medtronic iPro, DexCom and Freestyle Libre all have pro versions. More information is available on the following sites: 

What the CGM can do

Personal-use CGMs have programmable alerts and alarms to let you know when the glucose reading is:

  • Rising
  • Falling
  • Drops below a certain target
  • Rises above a certain target

Continuous glucose monitoring can also help people identify trends by tracking and logging different events like activity, stress, and meals and the corresponding glucose levels. This data can be uploaded to a web-based program or a desktop program to share with your healthcare provider.

Does using a CGM mean the end of finger pricks? 

Unfortunately, using a CGM does not mean the end of finger pricks. Using a CGM requires at least two (and some versions may require up to four) per day for something called calibrations. These calibrations are a double check system to make sure the glucose readings from the fluid under the skin are accurate.

The sensor itself is changed by the user every 7 days. One professional version is worn for 14 days and it does not require calibrations. However, the glucose readings cannot be seen until after the 14 days are over and the information is removed from the sensor worn at your doctor’s office.

CGM Comparison Chart

Click here to view pdf of chart.

Who can use a CGM?

  • Anyone who has diabetes may be eligible to use the professional version
  • Anyone with diabetes on insulin may be eligible for the personal version
  • Those with a dangerous condition known as hypoglycemia unawareness (does not have symptoms of low blood sugar)
  • Those with hyperglycemia (high blood sugar)

Is CGM covered by insurance?

A professional CGM may be covered by all insurance companies, including Medicare and Medicaid. A personal CGM is typically covered by most private pay insurance companies. 

Every version is different, so each CGM company can assist in determining the level of coverage. However, some state Medicaid plans will not cover the personal version. Check with your state. There are special requirements for Medicare coverage and only one version of a CGM will currently be available for coverage. Check with your healthcare provider. 

Those who are eligible include:

  • 3 or more insulin injections per day or wearing an insulin pump
  • 4 or more blood glucose tests per day
  • Documentation of both of the above in a doctor’s progress note in the last 6 months
Updated on: August 15, 2019
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