Continuous Glucose Monitoring Devices

Dexcom vs. FreeStyle Libre

Continuous Glucose Monitoring Devices (aka CGMs) have revolutionized the diabetes world. With a small sensor, they show glucose levels in real time, which allows wearers to make informed decisions about food, insulin, and exercise. The first CGM was FDA approved in 1999, and technology has come a long way since!

“Don’t you hate having something attached to you all the time?” is a common question I get when people see my CGM. But the truth is, I feel lost without it. I’ve been a faithful Dexcom user since 2015, but counsel many patients who use FreeStyle Libre CGMs. They’re both great options! Keep reading for pros, cons, and personal insights on each system.

Benefits of Continuous Glucose Monitoring

CGMs measure interstitial glucose (the fluid between your cells) every 1-15 minutes. This allows many CGMs to show glucose trends in real time, which is a game changer for people with diabetes. Here are a few benefits of wearing a CGM: 

• Identify blood sugar patterns throughout the day and night without fingersticks
• Predict and prevent high blood sugars
• Predict and prevent low blood sugars
• Learn how different foods affect your blood sugars
• Learn how exercise, stress, and illness affect your blood sugars

And, research shows that CGMs help people with diabetes reduce their HbA1c, a measure of blood glucose levels over time. Here are a few CGM systems that I have personal or professional experience with:

Dexcom G6 CGM

Dexcom released their first CGM in 2006. I’ve been using Dexcom CGMs since 2015, and their latest version, the G6, since 2018. The Dexcom G6 measures glucose levels every 5 minutes and is intended for wear on the abdomen for up to 10 days. It is considered the most accurate CGM on the market right now.

Check out my Instagram video showing how to apply a new Dexcom sensor.

Also, I’m a big fan of Skin Tac Liquid Adhesive to help keep my sensor in place.

Dexcom G6 Pros and Cons

Pros: accuracy; customizable alarms for high and low glucose levels

Cons: Longer warm-up period than FreeStyle systems; shorter wear time than FreeStyle; multiple components (sensor, transmitter, and receiver)

FreeStyle Libre 14 Day CGM

The FreeStyle Libre 14 Day CGM was released in 2017, and is a flash monitoring system, meaning you scan your device over the sensor to get a glucose reading. It is intended for wear on the back of the arm for up to 14 days.

FreeStyle Libre 14 Day Pros and Cons

Pros: simple application, with fewer steps than Dexcom; longer wear than Dexcom

Cons: must scan at least 4 times per day (once every 8 hours) for accuracy and to save data; does not give high/low glucose alerts; less accurate than Dexcom

FreeStyle Libre 2 CGM

The FreeStyle Libre 2 is the latest FreeStyle version available in the US. It is intended for wear on the back of the arm for up to 14 days and has customizable high and low glucose alerts.

FreeStyle Libre 2 Pros and Cons

Pros: simple application with fewer steps than Dexcom; 14-day wear; customizable high/low glucose alerts

Cons: slightly less accurate than Dexcom

FreeStyle Libre Professional CGM

The FreeStyle Libre Professional (Pro) CGM was released in 2016, and is a great option for people with diabetes who want a better understanding of their blood sugar patterns, but don’t want to wear a device long-term. It’s also a good tool for people on long-acting insulin only, or standing insulin doses. The FreeStyle Libre Pro is a small sensor worn on the back of your arm for just 14-days, without reapplication to provide a snapshot of your glucose patterns. It measures glucose levels every 15 minutes, but does not give real-time readings. Instead, the sensor is downloaded in your healthcare provider’s office.

FreeStyle Libre Professional Pros and Cons

Pros: No devices, no alarms, easy application and wear

Cons: does not give real time glucose readings; less accurate

CGM Comparison Chart

Feature	Dexcom G6	FreeStyle Libre 14 Day	FreeStyle Libre 2	FreeStyle Libre Pro
Duration of Wear	10 days	14 days	14 days	14 days
Application	Requires a little more dexterity to insert the reusable transmitter; button for auto-insertion (8 steps)	Push-down insertion (7 steps)	Push-down insertion (7 steps)	Applied by a healthcare provider; push down insertion (8 steps)
Alarms	Customizable alarms for high and low glucose readings	No alarms	Customizable alarms for high and low glucose readings	No alarms
Connectivity	Real time glucose shows on receiver or smartphone with the Dexcom G6 app. The Dexcom Clarity app shows glucose patterns for up to 3 months.	Flash monitoring on reader or smart phone with Freestyle LibreLink app. The LibreLinkUp app allows you to share readings with caregivers. The LibreView portal allows you to share with healthcare providers.	Real time glucose shows on reader or device smartphone with the Freestyle 2 app.	No real time glucose readings. Sensor is downloaded in an office by your healthcare provider.
MARD (aka accuracy – The lower the number, the better!)	9.0%	9.4%	9.3%	12.3%
Warm-up	2 hours	1 hour	1 hour	n/a
Reading Frequency	5 minutes	Scan at least once every 8 hours for improved accuracy	1 minute	15 minutes
Location of Wear	Approved for wear on the abdomen	Approved for wear on the back of the arm	Approved for wear on the back of the arm	Approved for wear on the back of the arm
Style and Size	Oblong, gray, with ½” of adhesive visible around the transmitter	Round, white, minimal adhesive showing; about the size of 2 quarters, stacked	Round, white, minimal adhesive showing; about the size of 2 quarters, stacked	Round, white, minimal adhesive showing; about the size of 2 quarters, stacked
Ages	Approved for ages 2+	Approved for ages 18+	Approved for ages 4+	Approved for ages 18+

*For more information or to request samples, visit each manufacturer’s website or talk to your healthcare provider*

Other Important Things to Know About CGMs

• CGMs measure interstitial glucose values, not blood glucose values. This means that there is often a delay (roughly 2-10 minutes) between your blood glucose and your interstitial glucose levels. 
• CGMs sensors should be removed before MRI, X-ray, or CT-scans. 
• These devices are not indicated for people on dialysis, yet. 
• High doses of vitamin C and aspirin may alter accuracy of glucose readings.
• See the manufacturers’ websites for other important safety reminders
• Every person with diabetes has a unique situation; always consult your healthcare provider about important medical decisions

Does Insurance Cover CGMs?

CGMs are largely approved by private insurance for people with type 1 diabetes, but be sure to check coverage on your specific plan. You may have a deductible or co-pay for durable medical equipment. Medicare covers CGMs for people with type 2 diabetes on intensive insulin management, defined as

• Blood glucose monitoring 4 or more times per day
• Insulin injections 3 or more times per day

Conclusions

Each of these systems has pros and cons, but at this time, my recommendation would be to go with either the Dexcom G6 or Freestyle Libre 2 because of their accuracy and alarms. And I say ‘at this time’ because as far as diabetes tech has come, even better technology is coming… The Dexcom G7 is currently available in Europe, and is 60% smaller than the G6, with just a 30 minute warm-up! The G7 is expected to be FDA approved in 2022, though no specific date has been given. And the Freestyle Libre 3 has been approved in Europe, with the benefit of an even smaller sensor! So much to look forward to!

I do not have hands-on experience with the Guardian, Eversence, or other CGMs, but would love to hear about your experience in the comments!