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CGM…is it for you?

As a diabetes educator in an inpatient hospital, my diabetic patients have been asking me about the “meter in the arm.” These patients are inquiring about the continuous glucose monitor (CGM). The CGM is a growing technology that can provide users hundreds of blood glucose values a day!

The CGM device collects blood glucose data every 1-5 minutes, depending on the device used. People love the fact that they can attach the sensor to their arm or abdomen to monitor their blood glucose. Depending on the device, they can leave the sensor there for 7-14 days. The Eversense device has a sensor that is implanted in the arm and gets changed every 90 days.

The sensor detects glucose in the interstitial fluid. The interstitial fluid is fluid just beneath the skin. This sensor glucose (SG) can be displayed as a number on a Reader, Smartphone, or Apple Watch, depending on the device. Users can even share the data with family or friends, which is ideal for parents with young children who want access to their child’s glucose readings while in school. Data can also be shared with Primary Care Providers by sharing a link.

The CGM results can help a person make decisions in their treatment and give advanced warnings if their glucose is going too low or too high. It can also improve diabetes self-management to see how exercise, medication, and diet can impact glucose control.

There are currently four CGM devices on the US market. They are Dexcom G6, Guardian 3, Freestyle Libre /Libre 2 plus the Eversense.

Dexcom G6

The Dexcom G6 has a sensor that is attached to the skin with an adaptor every 10 days. A transmitter lies on the top of the sensor and sends signals to a phone and /or an insulin pump. The FDA has approved its use on the stomach area, but many users report success on arms and legs.

Medtronic Guardian 3

Medtronic Guardian 3 is part of an insulin pump system. The Guardian Connect does not connect to any pump and the smartphone is used to view glucose readings. Both use the same sensors, just with different transmitters. It is FDA-approved to wear on the back of the arm or stomach area. Sensors need to be changed every 7 days.

Freestyle Libre 2

Freestyle Libre 2 system uses flash glucose monitoring by waiving the reader over the sensor to get a reading. The Libre 2 has optional alarm settings that can be turned on for highs and lows. Highs and lows are only captured when the reader is within 20 feet of the sensor. The sensor is changed every 14 days. This system is a popular lower-cost option. It is simple and easy to use.


The Eversense sensor is implanted in the arm by a trained professional in an office setting. The sensor is removed every 90 days and a new one is inserted in another site. A transmitter attaches to the skin with skin adhesive over the sensor insertion area. The transmitter is removable since it needs daily charging. This CGM provides an on-body vibration alert for low or high glucose levels even if your smartphone isn’t with you!

How can you get one of these devices?

How can someone get a CGM? You should have a conversation with your healthcare provider, or PCP, to see if the CGM is right for you and to receive a prescription. Some physician offices, particularly endocrinology offices, have professional CGMs. You can try the CGM for a few days and see how you like it. It will also give the provider a few days’ worth of glucose data to help in treatment decisions.

The Freestyle Libre has a free two-week program on their website. You provide the information online and they will let you know if you meet the requirements. If you meet their requirements, you will need a prescription from your healthcare provider and then you can pick up the CGM from your pharmacy. Please note that those on Medicare can’t use any free coupons for the CGM.

When to finger-stick.

Television advertisements want people to believe that finger sticks are not needed ever again with the CGM. However, there are times when you must do a finger stick. Here are some examples of when a finger stick is warranted.

  • A calibration or a blood symbol appears on the device (Eversense requires twice-daily calibration.)
  • Symptoms do not match the CGM reading.
  • Some devices take at least one hour to warm up.
  • The sensor falls off and you don’t have a replacement.
  • If you feel the CGM is inaccurate for any reason.
  • Confirm hypoglycemia reading or impending hypoglycemia (the arrow is pointing down on the Libre).
  • During times of rapidly changing glucose (more than 2mg/dL per minute).

There are some limitations on CGMs. For instance, they are not FDA-approved in pregnancy, dialysis patients, or critical care populations. The technology has been recently used during the pandemic in some ICU settings. However, the CGM is still a work in progress in the hospital, but we hope to see its use in the near future.
There is also a risk of increased distress with devices that cause multiple alarms which are known as alarm fatigue.

Some of the advantages include:

  • CGMs can be used with Type 1 or Type 2.
  • CGMs take the pain away from multiple finger sticks.
  • CGMs help those at risk for hypoglycemia such as athletes, the elderly, renal impaired (not on renal dialysis), and hypoglycemia unawareness (signs of low glucose are not felt).
  • CGMs help to reach A1c goals
  • Some CGMs can work alone or some can work in combination with the insulin pump.

Some issues to consider with CGM:

  • When traveling through airport security, ask for a pat-down, instead of the metal detector to prevent damage to the sensor.
  • Remove sensor for CAT Scans or MRI or X-rays. (Does not apply to the Eversense.)
  • Doses over 500 mg of Vitamin C falsely raise the glucose of the Freestyle Libre 2.
  • Aspirin may falsely lower glucose readings of the Freestyle Libre 14-day system.
  • Some people may have difficulty maintaining sensor adhesion.

My patients who wear a CGM say they love it! It takes away the pain from multiple finger sticks a day. The alarms give them a sense of security, knowing that they will get an alarm for glucose going too low when they are awake or asleep. Family members of older adults living alone or for those with young children, like the fact that they can get the shared glucose readings. For more information, you can go to their specific websites:

Dianna Morrow is a certified Diabetes Care and Education Specialist and Registered Nurse at Encompass Health Rehabilitation Hospital of York, Pennsylvania. Dianna is a co-facilitator of the Diabetes Protocol team at Encompass Health. She is also a member of the Diabetes Coalition of York County, PA.

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