CGM: Continuous Glucose Monitor


Continuous glucose monitors (CGMs) are tools used to measure glucose levels on a continuous basis. They give the wearer trend information about what those levels have been and where they may be heading.  CGM devices are currently available from manufacturers including Abbott, Dexcom, Eversense, and Medtronic. For people with Type 2 diabetes, CGMs can be a major step to consistent glucose monitoring, understanding their glucose trends, and keeping their levels in a safe and healthy range. This is especially key for people with Type 2 who take insulin, as a CGM can help monitor low glucose levels.

What is a CGM and How Does It Work?

A CGM is a small wearable device that tracks your glucose throughout the day and night. The wearable sensor communicates wirelessly with a receiver or smartphone. Some continuous glucose monitors notify you of your high and low glucose readings. Typically, continuous glucose monitors automatically check your glucose levels at least every 5 minutes. They measure interstitial fluid (ISF), a thin layer of fluid that surrounds the cells of the tissues below your skin, instead of glucose directly from your blood. To learn more about the differences between blood glucose readings and sensor readings, watch the video by FreeStyle Libre system below.

A CGM consists of three basic parts:

  • Receiver (or smartphone) –  A device where you can check your current glucose level, look at past data, and view your glucose trends and patterns. This may be an app on your smartphone or a separate device.
  • Sensor -The device that measures glucose. It contains a very thin wire that is inserted under the skin, but is typically painless to wear and remains in the skin for several days. Users wear them on the stomach and the back of the arms or legs, or according to the manufacturer’s instructions.
  • Transmitter –  Some CGM systems, like Dexcom, also have a small piece that fits onto the sensor. This reusable transmitter sends glucose data wirelessly to your display device.

For example, Abbott’s FreeStyle Libre 14-day system has a painless and water-resistant sensor worn on the back of the upper arm. The sensor measures glucose every minute. The handheld reader included with the system is used to “scan” the sensor. The scan provides current glucose readings, as well as 8-hour glucose history, trends, and the direction your glucose is likely to be heading. Declared as the longest lasting self-applied sensor on the market, one FreeStyle Libre 14-day sensor can be worn for up to 14 days.

The Benefits of Using a CGM

Pricking your fingers several times per day can feel like a chore. Here are some benefits to using a CGM to prick your finger less and understand your glucose levels better.

– Improved Glycemic Control 

Real-time insight into your sugar levels allows you to see how medication, food, exercise, and other activities affect your glucose levels. This means you can make adjustments to your diabetes self-management plan quickly and better convey any trends or concerns to your diabetes care team.

Research shows people with Type 2 diabetes who are on multiple daily insulin injection therapies (MDI) and used a CGM lowered their average A1C from 8.5 percent to 7.7 percent. In contrast, those who tracked their glucose using a standard BGM were only able to lower their A1C from 8.5 percent to 8.0 percent.

Also, of course, better control over your glucose reduces the risks of long-term diabetes complications.

– Notifications for Hypo- or Hyperglycemic Levels

Continuous glucose monitors can tell you when your glucose is trending too high or low, which can signal hyper- or hypoglycemia. You can set these notifications in your device.  For instance, you can tell your device to notify you when your glucose levels are reaching 80 mg/dL or lower or spikes to 200 mg/dL or higher. Eversense, a CGM that is implantable and designed for long-term use, sends alerts before you experience a high or low glucose event. Eversense’s alerts can be visual, auditory, and on-body vibe alerts, even during sleep.

– Smartphone Capability 

Some CGMs have apps available to both iPhone and Android users that function through bluetooth capability. The FreeStyle LibreLinkallows wearers to get real-time glucose information to their iPhones. The app provides insight into glucose trends and patterns, current glucose readings, and entry for food, insulin use, exercise, and other things that impact glucose numbers. It’s compatible with the iPhone 7 or later running iOS 11 and later.

Eversense’s and Dexcom’s respective mobile apps allow you to invite up to 5 friends and family members to view your glucose data.

The benefits of a CGM can make life with Type 2 diabetes easier by removing the guesswork out of closely monitoring your glucose levels. Without worry, you’ll be able to know your levels right away. You can easily predict if you are going to be heading high or low due to the trends shown on the device. With this knowledge, you can actively prevent potentially dangerous situations in glucose management.

– Diabetes Data Management Software 

Need to print the data from your device for your next doctor’s appointment? You’re in luck, as some CGM companies have diabetes data management software where you can view and print standardized reports about your glucose history. The Dexcom CLARITY  app lets you stay one step ahead by providing weekly notifications of trends and statistics about your glucose numbers. Their standardized reporting feature shows the big picture of your diabetes management. Finally, Dexcom’s CLARITY app users can compare glucose data to evaluate improvement or problem areas over time.

Usage Tips

Continuous glucose monitors are meant to stick to your skin for several days. If you find the adhesive part of your CGM wearing off, follow the manufacturer’s instructions on how to replace it. You can also ask the manufacturer if you can purchase adhesive wipes to ensure the long-lasting wear of your device. Avoid placing your CGM at spots where your body naturally bends or where clothing might cause irritation.

How Do I Get a CGM?

CGMs require a prescription for use, so talk to your doctor about your device options and decide together which might be best for you. Check what brands are covered under your insurance plan (including patients on Medicaid and Medicare). For example, Dexcom’s CGMs are covered by Medicare. To receive a CGM under Medicare or Medicaid, please contact your local state health exchange to check your eligibility.

You’ll also want to see if your preferred CGM brand offers a complimentary prescription retrieval service. For example, FreeStyle Libre’s prescription retrieval service informs your healthcare professional about the FreeStyle Libre 14-day system, requests a prescription directly from your healthcare provider, and notifies you when your prescription has been sent to your pharmacy.