Continuous glucose monitors (CGMs) have evolved over the years, and there have been exciting improvements in the accuracy, reliability, and ease of use for these devices. However, there are some specific differences between the two main types of CGMs, real-time and intermittently scanned, that you may want to consider when choosing a system that’s right for you

Real-time CGMs

These systems are made up of three components: the sensor (a small wire catheter that is inserted under the skin on your arm or abdomen), a transmitter that attaches to the sensor, and a handheld receiver and/or smartphone that displays your glucose data in real time.

The Pros

1. Offers alerts. The most significant benefit of all real-time CGM systems is having audible alarms that can warn you if your blood sugar (blood glucose) is getting too high. This allows time for adjustments that could lessen the impact of high or low blood sugar or avoid it altogether. 
2. Transmits data continuously. With real-time CGM devices, data is constantly pushed to a receiver or smartphone without the need for additional action, such as a finger prick.  
3. Shares data. The ability to share data with family members and friends is another important feature. It acts as a safety net, especially when traveling. For example, if you don’t wake up to a low glucose alarm during the night, someone else will be alerted and can get in touch with you. 
4. Eliminates finger sticks. While not all real-time CGMs offer this benefit, some allow you to make treatment decisions—how much insulin to dose, for instance—without the need for finger-stick confirmation. Plus, some are factory calibrated, eliminating the hassle and pain of calibrating with finger sticks.

The Cons

1. Requires setup. To use the alarm and alert features, you have to program your settings, such as your low glucose threshold and target ranges. This can get a little complicated, especially if you don’t read the instructions. However, the manufacturers offer online video tutorials to guide you through the process. Your diabetes care team, particularly your diabetes educator, can help you learn to use your device.
2. Alerts can be tiresome. Some people complain about the repeated alarms (real or false). It can become so bothersome—or embarrassing, depending on where you are or who you’re with—that they simply turn off the alarms altogether. However, this is mainly a problem with the older CGM systems, which are not as accurate as the newer ones.
3. Devices can be expensive. Although they are covered by most insurance companies and Medicare, they may not be affordable if you have to pay out of pocket. If cost is an issue, know that many device manufacturers offer patient assistance programs. You can find resources and contact information at InsulinHelp.org.

Updated Medicare Coverage Requirements for CGMs

Medicare has eliminated the four-time-daily fingerstick testing requirement for continuous glucose monitor (CGM) coverage! Read on to learn about how the American Diabetes Association championed this effort and what it means for your Medicare coverage moving forward. 

Learn More

Intermittently scanned CGMs

This system requires you to scan the device to get your glucose data. It uses two components: a combined glucose sensor/transmitter (inserted in your upper arm) and a separate touchscreen reader device. The sensor continuously samples and measures glucose levels, generates a new glucose value every minute, and records the reading every 15 minutes for 10 to 14 days of sensor wear time, depending on the model.

The pros

1. Convenient and easy to use. The sensor, which is about the size of two stacked quarters, is painless to apply, comfortable to wear, and easy to use. And you can scan the transmitter through your clothes, a real benefit when you want to be discreet.
2. Affordable. They are much less expensive than real-time CGM devices, and they are covered by most insurance companies and Medicare.
3. Shares data. Your glucose values can be shared in real time with up to 20 family, friends, caregivers, or health care providers using their smartphones. 
4. Eliminates finger sticks. Like the real-time CGMs, some intermittently scanned CGMs can be used to make treatment adjustments without the need for finger-stick confirmation, and some are factory calibrated, eliminating the hassle and pain of daily calibration with finger sticks.

The cons

1. Offers no alerts. There is a lack of alerts to warn about current or upcoming glucose problems. Without the chime of a CGM alarm, people with low blood sugar (hypoglycemia) unawareness may not know they’re low until their judgment is impaired. This also means you won’t be woken by a low-glucose alarm—a downside for anyone concerned about overnight lows.
2. Requires intent. You have to remember to wave the reader over the transmitter, which might not happen on days when you’re busy or distracted, or at night. And there’s a price for forgetting: The sensor can provide glucose values for 10 to 14 days (depending on the model) if you scan at least every eight hours. If not, the glucose information that is older than eight hours will be overwritten and not available for decision-making or download.
3. One version takes 12 hours to warm up. When a new sensor is inserted, the device will not show any glucose data for the first 12 hours. During this time, you will need to do finger-stick checks. 
4. Offers no option to calibrate. You cannot recalibrate the sensor when glucose values don’t match your finger-stick results. When your sensor and finger-stick glucose readings don’t match, it may mean your meter is inaccurate. Or it could indicate that your blood sugar is rapidly rising or falling. But it could also point to an inaccurate CGM sensor. Without the ability to recalibrate the sensor, you may need to insert a new sensor before its indicated wear time has expired.

How to choose?

Take the time to investigate both options and talk to your doctor and diabetes educator, who can provide valuable guidance and insights about the type of CGM system that may be right for you. They can also help you make the transition to a CGM and provide training to help you learn how to interpret and use your data to make appropriate treatment decisions and achieve your blood sugar goals.