Which CGM for Which Diabetes Patient?

Anne L. Peters, MD


February 12, 2018

Editorial Collaboration

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My last video on continuous glucose monitoring prompted several questions, so I want to try to clarify how I believe these devices should be used clinically. In particular, I will discuss the Dexcom and the Abbott FreeStyle Libre.

Both of these products are continuous glucose monitors (CGMs), and both are designated by the US Food and Drug Administration as replacements for finger sticks, which means that people can calculate their insulin dose from the glucose values they obtain from the CGM. With both devices, however, a backup finger stick should be available in case there is some discordance between the clinical setting and the glucose value from the CGM.

The Dexcom has been available for the longest period of time. It requires the patient to check the finger-stick blood glucose level twice a day to calibrate the device. The Dexcom then "speaks" to a receiver or to a smartphone and transmits the glucose level to the Tandem t:slim insulin pump and, in the future, to other devices.

The Dexcom provides alarms and alerts to patients to let them know if their glucose levels are going high, if they are falling fast, and if they reach a certain low level or a certain high level. Specific levels can be programmed into the device by the patient. It gives these alarms to the patient and to people who are following the patient, in real time.

In my opinion, that is the real beauty of the Dexcom. Not only does it tell patients their glucose levels, but it notifies them if they are about to get into trouble.

The FreeStyle Libre is factory calibrated, so people don't have to calibrate the device. The Libre only talks to you when you "wand" or scan it with the reader. Patients can check their glucose levels anytime they want to by wanding the reader over the sensor. By doing that, patients can see if their glucose levels are going up, down, or staying the same. The Libre backfills so that a patient can see the glucose values for the past 8 hours.

The Libre, however, does not have alarms and alerts; a person is not alerted if their glucose level is too low or too high. Interestingly, some patients who have tried the Dexcom do not like those alerts; I personally think they are quite useful.

But there is no "one size fits all" when it comes to continuous glucose monitoring. These devices have differences, and that may be the most important thing I can tell you. So, if I have a patient with type 1 diabetes who is using a Dexcom and is doing well, I am not going to switch them to the other device. I believe that it is a great tool for some people. Anyone who is on a complicated insulin regimen and is at risk for hypoglycemia will receive an alert or alarm when the blood glucose levels change. I love that feature.

On the other hand, the Libre is simpler, less expensive, and is factory calibrated. I certainly have patients who do not want to use the Dexcom and who really like the Libre. It gives them data that they never had before, and I can download the device in the clinic to get all of the same retrospective data I get with the Dexcom.

If a patient is using a Dexcom and it works well for the patient, you should not change to the Libre. And if a patient with type 1 diabetes wants a Libre, that is also fine.

The Libre has expanded my use of continuous monitoring to my patients with type 2 diabetes because it does not require as much education or calibration. I can put a Libre on patients with type 2 diabetes and get more data than I used to have, whether I use the professional version or the personal version.

Both CGMs are great tools, and both fill a very important role. There is a synergy between the two of them. We may have patients who switch from one to the other. The point is that they are both options for our patients. You need to discuss these with the patients you believe are suitable candidates for continuous glucose monitoring and let patients use the device they find is best for them.

I am very excited about both of these devices. I am glad that they are on the market and I am glad that our patients have the choice. Thank you very much.


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