October 23, 2020

CGM Systems: Tips for Selection and Use

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CGM Systems: Tips for Selection and Use

Curtis L. Triplitt, Pharm.D., CDCES

Clinical Associate Professor, Medicine/Diabetes, University of Texas Health Science Center at San Antonio, Associate Director, Diabetes Research, Texas Diabetes Institute, University Health System, San Antonio, Texas

Curtis L. Triplitt, Pharm.D., CDCES, is Clinical Associate Professor of Medicine, Division of Diabetes and Clinical Assistant Professor of Pharmacy at the University of Texas Health Science Center at San Antonio. Dr. Triplitt practices at the Texas Diabetes Institute, where he manages patients with an endocrinologist and is involved with diabetes and metabolism research. 

Dr. Triplitt received his Doctor of Pharmacy degree from the University of Texas Health Science Center at San Antonio and the University of Texas at Austin. He completed an ASHP-accredited primary-care residency at the William S. Middleton Memorial Veterans Hospital in Madison, Wisconsin.

Dr. Triplitt is the Editor-in-Chief of Diabetes Spectrum and past Vice-Chair of the Texas Diabetes Council, Texas Department of State Health Services. He has served as an investigator on multiple clinical trials focusing on type 2 diabetes, including the effects of medications on insulin sensitivity, glycemic control, and hypertension, and he has published over 50 peer-reviewed articles and 10 book chapters on diabetes. In 2008 he was honored as Pharmacy Preceptor of the Year for the University of Texas. Dr. Triplitt lectures at both the national and statewide levels concerning diabetes and has been involved with the development of multiple clinical treatment algorithms for the prevention and treatment of diabetes in the State of Texas.


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I am sure you are aware of recent advances in technology used by patients with diabetes, but maybe you haven’t had time to take a closer look at them. With that in mind, I’m going to concentrate on a couple of things I’ve observed more frequently. First, I’ve noticed an uptick in the number of continuous glucose monitors (CGMs) being prescribed and dispensed by pharmacists, which puts us in a unique position to help patients with diabetes optimize their use of this technology. Second, a fair number of patients who start on CGM stop using it at some point for a variety of reasons. It is not a difficult technology, but if patients are not taught the basics, including how to do simple troubleshooting, they can become frustrated and quit using CGM. Let’s discuss some tips that might help our patients stay the course.

Choosing a CGM System

We as pharmacists may not get to choose a patient’s CGM system, but if you are involved in this process, it is imperative to find out whether the system is covered by the patient’s insurance. Most insurance companies will cover CGM if the patient is on multiple daily injections of insulin. CGM is not likely to be covered if the patient is only on oral medications. Four companies make personal CGM systems, but only the Freestyle Libre 10 and 14 and Dexcom G6 are dispensed from the pharmacy.

Accuracy is comparable among the CGM systems. CGM measures interstitial glucose, which lags 10-15 minutes behind the blood glucose. This can be of concern if the blood glucose is rapidly changing or if hypoglycemia is present. Always advise patients to check their blood glucose if they are not sure of the accuracy of a CGM reading.

The Freestyle Libre is an intermittent scan CGM. Therefore, if the user does not scan (place the reader within a couple inches of the sensor) at least every 8 hours, there is a loss of older data after 8 hours. It is available in a 2-part system with sensor (10- or 14-day wear time) and a reader/app. For patients who pay cash for CGM systems, Freestyle Libre is the least expensive option, with the 14-day sensors being slightly more expensive than the 10-day sensors. No fingerstick calibrations are needed. Also, warm-up times from placement of the sensor until readings can be obtained are different (10-day: 12 hours; 14-day: 1 hour). Freestyle Libre 2 was approved this year. It has a 14-day wear time and 1-hour warm-up period, and it can be set up for individualized alarms for high and low glucose readings.

Dexcom G6 is a true CGM with no scans necessary to get glucose readings continually delivered to the reader/app. It is available as a 3-part system with a sensor (10-day wear), a transmitter that snaps in over the sensor (3-month use), and an app to read the data. Warm-up time is 2 hours, and it has alarms that can be individualized for when high and low glucose readings are detected.

Keeping the Sensor On

A common problem with CGM devices is dislodgment of the sensor prior to the full sensor wear time. Once the sensor is dislodged, it cannot be used again. Dislodgement can happen by either a physical means, such as hitting a door edge or a rubbing seatbelt, or failure of the sensor adhesive.

Placement of the sensor is key for avoiding physical dislodgement. In our clinic, we recommend placing the sensor on one of three places: back or inner part of the upper arm, abdomen (above the position where it could be jostled by a seatbelt), or upper thigh (usually outer part, unless the patient anticipates maximum protection on the inner part). Talk with the patient to determine which placement option is best for his or her lifestyle. Key factors to consider include activities, need for discretion, and comfort, among others.

Many people use additional measures to keep the sensor secure since sweat, moisture, and just life can deteriorate the sensor’s adhesive. We recommend that patients shave the area where the sensor will be placed, use an alcohol wipe and let dry, then use a wipe-on medical adhesive (such as Skin Tac) where the sensor will be placed.  They may also cover the sensor with a transparent dressing or medical tape if needed. Additional information for addressing skin and adhesive issues is available.1

Another common issue is skin irritation. Skin irritation can be managed by rotating sensor sites. We recommend letting the affected skin rest for several weeks before the site is used again. In addition, if skin irritation is particularly bad, though not recommended by manufacturers, a barrier film can be applied before the sensor is placed, which will prevent direct contact of the sensor adhesive to the skin.

Alternative Site Placement

The Dexcom CGM is approved for placement on the abdomen or upper buttocks, and the Libre iCGM is approved for placement on the upper arm. We have also had good success with Dexcom in the upper arm and thigh and the placement of Libre on the thigh. It is important that the sensor not be placed where the person could potentially “compress” it while sleeping. Patients should be educated about the fact that compression of the sensor might result in falsely low blood glucose readings. Should the sensor dislodge or stop giving accurate readings before the end of the sensor period, the manufacturer may give a replacement sensor to the patient. However, if the patient has placed the sensor on a non-approved site and relays that information to the manufacturer, the manufacturer may refuse to replace it.


As CGM use continues to increase, we as pharmacists need to teach our patients to use these systems properly and help them troubleshoot problems that can occur with the sensors.

More Information


  1. Englert K, Ruedy K, Coffey J et al. Skin and adhesive issues with continuous glucose monitors: a sticky situation. J Diabetes Sci Technol. 2014; 8:745-51.