Continuous Glucose Monitors: Options, Features, and Tips
In the past 20-plus years since the release of the first continuous glucose monitor (CGM), the use of these devices has grown significantly. Advances in technology have improved their accuracy and ease of use, and insurance coverage has expanded.1
For many people, CGMs have taken the place of blood glucose monitors. They provide glucose readings every 1 to 5 minutes and trend arrows, which helps the user understand the direction their glucose is going (up, down, or steady).
Users are able to see how different foods and activities impact their glucose levels. This information can help them increase their time in range and reduce the frequency and duration of hypoglycemia.
Continuous glucose monitors
The following brands of CGMs are available in the United States:
- Dexcom G6
- Abbot Freestyle Libre models (Freestyle Libre 14, 2, 3)
- Medtronic Guardian Connect
- Senseonics Eversense E3
Here are a few features of each. The lower the mean absolute relative difference (MARD), the more accurate the CGM reading.
The system components include a sensor, sensor applicator, transmitter, and display device. The sensor is replaced every 10 days, and the transmitter is used for 3 months. Glucose data is viewed on the Dexcom G6 smartphone app or on the Dexcom G6 Receiver. Each new sensor session requires a 2-hour warm-up.2
If a sensor code is used, calibration is not required. The frequency of glucose readings is every 5 minutes. The MARD is 9 percent.2
The alerts included on the Dexcom G6 are:
- Urgent low
- Urgent low soon
- User-programmed high alert
- User-programmed low alert
The Dexcom Follow app, is used to share glucose data with family and friends. Dexcom Clarity is a diabetes management application used to share your glucose data with providers.
Abbot Freestyle Libre models
The following information pertains to the Freestyle Libre 14, Freestyle Libre 2, and Freestyle Libre 3 monitors. The system components include a sensor, sensor applicator, and smartphone app. The sensor is replaced every 14 days. Glucose data is viewed on the LibreLink smartphone app or Reader Device. Each new sensor session requires a 1-hour warm-up.3
Calibration is not required. The frequency of glucose readings is every 1 minute. Glucose is only visible if the user scans the sensor with their LibreLink app or Reader Device. The MARD on the Freestyle Libre 2 is 9.2 percent.3
The alerts included on the Freestyle Libre models are:
- Low glucose reading
- High glucose reading
Alerts/alarms are optional and are only available with Freestyle Libre 2 and Freestyle Libre 3.
Also available is LibreLink Up, which is used to share glucose data with family and friends. LibreView is used to share your glucose data with providers.
Medtronic Guardian Connect
The system components include a sensor, reusable sensor insertion device, transmitter, transmitter charger, and smartphone app. The sensor is replaced every 7 days. Glucose data is visible on the Guardian Connect smartphone app. Each new sensor session requires a 2-hour warm-up.4
Calibration is required every 12 hours. The frequency of glucose readings is every 5 minutes. The MARD on the Guardian Connect is 10.6 percent when placed on the abdomen and 9.1 percent when placed on the arm.4
The alerts included on the Guardian Connect are:
- Urgent low alert
- User-programmed high alert
- User-programmed low alert
- Predictive alerts 60 minutes before a high or low glucose
Guardian Connect is used to share glucose data with family and friends via Care Partner. Carelink is used to share your glucose data with providers.
Senseonics Eversense E3
The Senseonics Eversense E3 is an implantable sensor. The sensor is placed just below the skin in the subcutaneous tissue. It requires a short procedure at your doctor's office. The system components include an implantable sensor, transmitter, and smartphone app. The sensor is replaced every 180 days. Glucose data is viewed on the Eversense CGM smartphone app. Each new sensor session requires a 24-hour warm-up.5
Calibration is required every 12 hours. The frequency of glucose readings is every 5 minutes. The MARD is 8.5 percent.5
The alerts included on the Eversense E3 are:
- High alert
- Low alert
Eversense Now and My Circle are used to share glucose data with family and friends. Eversense Data Management System is used to share your glucose data with providers.
When applying your CGM, ensure that the area of your skin is clean, hair-free, and dry. Use adhesive aids, such as Skin Tac, and bandages.
If there are issues with losing a connection, move the display device (the receiver or smartphone) closer to the sensor. Reset Bluetooth if using a CGM app on your smartphone by turning off Bluetooth, waiting a few minutes, then turning Bluetooth on again.
The CGM reading doesn't match the blood glucose meter reading
There may be a more significant difference between your CGM reading and your blood glucose meter reading if the trend arrows on your CGM show that glucose is rapidly increasing or decreasing. Trend arrows typically show a more rapid rate of change following a meal or during physical activity.
CGMs and blood glucose meters measure glucose in different body fluids, which means glucose levels should be close but will likely not be exact. Up to a 20 percent difference in the readings is often considered acceptable.
Sometimes, the CGM needs calibration. To calibrate the CGM, check your glucose with a blood glucose meter and enter the exact number into the CGM display device or smartphone app.
Speak with your doctor or diabetes educator to find a CGM device that fits your individual needs and goals, and contact your insurance company to see which devices are covered by your plan. If you plan to use your smartphone to view glucose data, ensure your phone is compatible with the CGM app. Each website provides a list of compatible devices.
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