Continuous glucose monitoring, known as CGM to people with diabetes (PWDs), has the potential to change lives and bring fresh insight into how one manages this condition.
But what are the best CGM options and how do they compare?
The two most popular CGMs available in the United States as of spring 2021 are the Dexcom G6 and Abbott FreeStyle Libre.
Here is DiabetesMine’s detailed comparison of these two systems, including how they each work, what makes them different, how accurate they are, and how much they cost.
“(Users) can learn a lot about the impact of lifestyle on glucose values, such as food intake, amount and quality of sleep, or type of exercise. That can be very eye-opening for the patient and motivate them to change behavior to improve glucose values,” said Rachel Stahl, a registered dietitian and diabetes care and education specialist (DCES) at New York-Presbyterian and Weill Cornell Medicine.
San Diego-based Dexcom G6 has been manufacturing CGM technology since its inception in 2005, and its sensors are designed to become more accurate, reliable, and convenient with each upgrade. The current Dexcom G6 model, which is approved for use in ages 2 and older, has been available since 2018, and the new Dexcom G7 is expected in 2022.
From its earliest model to the latest mobile connected device, Dexcom G6 has cemented its spot as the most popular full-featured CGM available.
How does it work?
The Dexcom G6 has two parts that click together and are worn on your body as a single unit: the sensor and transmitter.
10-day sensor. Each sensor comes housed in a plastic white and orange auto-inserter. A single-push button inserts the sensor’s tiny cannula into your skin and adheres the unit to your body with a built-in medical adhesive.
The sensor is water-resistant so can be worn in the shower or while swimming. It is FDA-approved for wear on your abdomen and upper buttocks. The sensor is built to last for 10 days before it automatically shuts off, though sometimes sensors fail early. In this case, the company will ship customers a replacement.
Transmitter. This little gray plastic oval is the brains of the system. It clicks into the clear plastic bracket of the sensor once inserted on your skin. Each transmitter has a 3-month battery life and is meant to be disposed of once depleted. Every 5 minutes, the G6 transmitter sends glucose readings via Bluetooth connectivity (with a range of approximately 20 feet) to a smartphone app or a separate handheld touchscreen receiver where the user can view the data.
Warmup time. The G6 has a 2-hour warmup before the sensor starts generating glucose data.
No “required” fingersticks. Even though the G6 is factory-calibrated and doesn’t require any fingersticks to confirm a glucose reading, some PWDs still opt to double-check their readings with a traditional fingerstick meter. The G6 does allow users to “calibrate” the system by logging a fingerstick result. This can sometimes help keep the CGM on track.
Programmable alerts. You can set your glucose alert ranges for high and low ranges, and set your preferences for audible or vibration alerts for different times of day or night.
There are “Do Not Disturb” and “Snooze” features on most alerts, although those options are disabled on important alerts like “Urgent Low Soon” and “Sensor/Transmitter Failure.”
The “Urgent Low Soon” alert is a non-optional warning whenever the sensor picks up that glucose levels are falling fast and predicts you’ll drop to 55 mg/dL within 20 minutes.
Mobile app control. Most G6 users no longer need a receiver, but opt to control and view the CGM via the company’s mobile app, which works with most iOS and Android phones (check compatibility here). The app home screen displays a circle with the current real-time glucose level and appropriate gray/red/yellow color code depending on whether you’re “In Range,” “Low,” or “High.”
The circle also has an arrow that points in the direction you’re trending, and below that is a graph showing 3 hours’ worth of glucose data in a dotted line. Want to view more than the past 3 hours of CGM data? Turn your smart phone horizontally to see up to 24 hours of data and scroll back accordingly.
Data analysis. The Dexcom G6 mobile app is designed to allow people to see glucose trends for the past 1, 3, 6, and 12 hours. But to review more comprehensive data, people can use the Dexcom CLARITY platform. You can access it online, or directly on your phone by clicking on the little green icon from the G6 mobile app, displayed in the top right corner of the horizontal view. Users can also grant access to share data with their healthcare professionals.
Remote monitoring. A built-in feature in the Dexcom G6 app allows remote viewing of data and trends by up to 10 authorized followers, who can monitor a user’s glucose readings in real time.
Interoperability. What’s unique to Dexcom G6 right now is the integration of its CGM with insulin pumps such as the Tandem t:slim to create a “closed loop” system that can automatically adjust insulin amounts based on glucose readings. Dexcom G6 will also work with the new OmniPod 5 tubeless patch pump expected later in 2021.
How accurate is it?
The standard measurement of CGM performance is known as the mean absolute relative difference (MARD). With this measure, the lower the number, the better the accuracy. Clinical data for the Dexcom G6 shows it has a MARD of 9 percent with sustained accuracy over the time a sensor is worn.
This is slightly more accurate than the FreeStyle Libre 2, according to the clinical study results. However, individual users’ experiences may vary, and many PWDs who have used both Dexcom G6 and FreeStyle Libre 2 report comparable accuracy.
How much does it cost?
The total cost of any CGM system depends on supply needs and the type of insurance coverage the user has.
Start by checking your insurance plan’s coverage of CGM. This will include whether they cover purchase at your local pharmacy, require a mail-order distributor, or whether they classify CGM as “durable medical equipment” (DME). DME may require a higher deductible before your insurance coverage kicks in.
Dexcom G6’s CGM has traditionally been classified as DME for most insurance plans, but it’s now becoming more common for the Dexcom G6 to be available through pharmacies.
Not all insurance providers have yet embraced this shift, which may offer cost savings with only needing to pay a single flat copay.
Remember, there are two separate pieces of hardware needed to use the Dexcom G6: transmitter and sensors, both of which require a prescription and have different price tags attached.
If purchased at retail cost from Dexcom G6 with most commercial insurance plans, the costs are (as of March 2021): a total of $237 for the G6 transmitter, that lasts 3 months, and a total of $349 for a three-pack of sensors (30 days’ worth).
At national pharmacy chains like CVS and Walgreens, cash prices vary but most locations queried by DiabetesMine quoted the price for a G6 transmitter at just under $300, and roughly $400 for the three-pack box of G6 sensors.
You can also purchase a Dexcom G6 with a prescription at Costco Pharmacy, as long as you are a Costco member ($60 annual fee) and sign up for their free pharmacy program. Prices are less expensive here:
- G6 transmitter: a total of $146.04 each
- Three-pack box of G6 sensors: a total of $318.54
Note that you may see online search results showing varying price points, based on now-defunct early Costco Pharmacy discounts. Since Costco discount prices are periodically adjusted, be sure to check in advance of driving to the store to purchase.
Medicare also covers the Dexcom G6 for those on certain “intensive insulin therapy” regimens, and eligible PWDS often see a “bundling” of their CGM and diabetes supplies including test strips. Pricing varies depending on one’s Medicare plan and any supplemental insurance coverage the user may have.
Abbott Diabetes first brought its FreeStyle Libre to the United States in 2017, and since mid-2020 the FreeStyle Libre 2 model has been available. It is FDA-approved for use in kids as young as 4 years old as well as adults with either type 1 or type 2 diabetes.
How does it work?
14-day sensor. FreeStyle Libre 2 uses a round, fully-disposable sensor the size of two stacked quarters, worn on your upper arm for best results. A sticky adhesive on the back side keeps it attached to your skin. It is also fully water resistant like the Dexcom G6 sensor.
It’s approved to last 14 days until you need a new sensor (4 days longer than Dexcom G6). Just like with Dexcom G6, Abbott’s tech support can assist in replacing a sensor that doesn’t last as long as it should.
Not continuous. What’s different is that although the FreeStyle Libre 2 is generally referred to as a CGM, it is not designed to beam real-time data like the Dexcom G6 does. Instead, it’s technically a “Flash Glucose Monitor,” meaning users have to manually swipe the FreeStyle Libre 2 handheld reader over the sensor to get glucose readings, as often or as little as they choose.
Handheld reader. Glucose results are sent to the handheld reader, a blue device that resembles a traditional glucose fingerstick meter. It measures 95mm tall x 60mm wide x 16 mm thick, and weighs 645 grams. It has built-in Bluetooth Low Energy, which is important because that allows for optional glucose alerts for high and low readings — unlike the earlier FreeStyle Libre model that did not offer alerts.
No fingersticks at all. Like Dexcom G6, the FreeStyle Libre 2 is FDA-approved for use without the need for backup readings from a fingerstick meter to confirm accuracy.
Warmup time. FreeStyle Libre 2 has a 1-hour warmup period before it starts generating glucose data. That’s a full hour shorter than the competing Dexcom G6.
Optional alerts. With the FreeStyle Libre 2, you can turn on optional alerts that can beep or vibrate to notify you about high or low glucose readings. The thresholds are programmable from 60 to 100 mg/dL to trigger a low alert, and 120 to 400 mg/dL for a high alert. While these alerts activate without a need to scan the sensor, you still need to scan the sensor to get an actual glucose result.
The ability to set alerts can be a deciding factor for many PWDs in considering different CGMs. Setting up alerts is particularly important for people who are worried about safety overnight. At night, low blood glucose levels can be even more dangerous as people often don’t feel symptoms or wake up in time to treat themselves properly.
Limited mobile app. The FreeStyle Libre 2 does not send readings to a mobile app, as that functionality is still under review by the FDA, meaning users can currently only scan using the handheld reader.
Data analysis. The data can be analyzed on the reader, or on a smartphone using the company’s FreeStyle LibreLink app.
Remote monitoring. The FreeStyle LibreLink app also offers remote data sharing with up to 20 people, twice as many as Dexcom G6.
Interoperability. FreeStyle Libre 2 is not currently compatible with any other diabetes devices, although it is being tested with other devices, including the future connected insulin pen system from Bigfoot Biomedical, for one.
How accurate is it?
This latest FreeStyle Libre 2 has a 9.3 percent total MARD score (9.2 percent for adults, and 9.7 percent for children). That means it’s not quite as accurate as the competing Dexcom G6, according to clinical data results.
How much does it cost?
Here are the approximate prices for the FreeStyle Libre system, largely available through pharmacies:
- With commercial insurance, Abbott reports that most of its customers pay between $10 and $75 per month for FreeStyle Libre 14-day sensors at participating pharmacies.
- The official list price is $54 per sensor, according to Abbott, although retail pharmacies like Costco and Walgreens quote prices of $58 to $69.
- The handheld reader runs $70.
- Users can opt to use the FreeStyle LibreLink mobile app for iOS or Android for no charge.
Abbott does not sell this device directly, but it can be ordered through your healthcare professional. The company began building out its channel for pharmacy purchase in 2020.
The cost for FreeStyle Libre 2 is clearly hundreds of dollars below the cost of a Dexcom G6 system, and affordability has been one of the big marketing points for FreeStyle Libre since the get-go.
|Dexcom G6||Abbott FreeStyle Libre 2|
|cost||roughly $3,800/year pre-insurance||roughly $2,300/year pre-insurance|
|how it scans||tiny built-in needle tests interstitial fluid, sensor is FDA-approved for wear on abdomen, upper buttocks||tiny built-in needle tests interstitial fluid, sensor is FDA-approved for wear on your upper arm|
|frequency of glucose readings||takes automatic readings every 5 minutes||user must waive the handheld reader over the sensor to get a glucose reading|
|sensor wear time||10 days||14 days|
|alerts and alarms||customizable and predictive alarms, including mandatory “Urgent Low Soon” alert||optional alerts for existing high and low alerts only|
|accuracy||9 percent MARD (lower MARD scores indicate better accuracy)||9.3 percent MARD|
|data review options||view trends on the app + CLARITY software for full data analysis||basic data on the handheld reader + FreeStyle LibreLink app for viewing trends|
Lizz Baldyga, who lives with type 1 diabetes (T1D) in Massachusetts, started out using the FreeStyle Libre for 2 years before eventually switching to the Dexcom G6 because of concerns over accuracy. She found that the FreeStyle Libre was frequently off by 100 mg/dL points, but that isn’t what she’s experienced with the G6, and she prefers the continuous nature of it compared to the need for manually scanning to get a result.
“I love that the Dex reads automatically, so I can just glance at my phone and see a reading,” she tells DiabetesMine. “I also love the alarms, which (the first-generation version) didn’t have as an option when I switched. I’ve seen my A1C drop a bit as well since switching to Dex, and that’s a big win for me.”
Michigan T1D Michelle Bates-Phipps, who was diagnosed in her 20s in 1991, says she started off using the earlier Dexcom G5 model with an integrated insulin pump back in 2017 and eventually upgraded to the G6.
But despite how much she loved the Dexcom G6 — particularly the glucose trend-spotting and being able to share data with her husband and doctor — it was too expensive because her insurance only covered 50 percent of her total costs. Depending on the supplier she used, the Dexcom G6 was costing her $180 to $200 per month, she says.
So, she switched to FreeStyle Libre, which is much more affordable as it’s covered better by her insurance plan.
“FreeStyle Libre gives me most of the tools that Dexcom G6 did at just over one-fourth the price,” she says. “Dexcom G6 has more bells and whistles, and I experienced less sensor failures than with FreeStyle Libre, but it does what I need it to.”
Until the FreeStyle Libre 2 mobile app is approved for the United States, Bates-Phipps says she’ll continue using the previous model of FreeStyle Libre with the 14-day sensors, so she doesn’t have to keep a separate handheld receiver charged to scan the sensors.
Lauren Plunkett, a DCES in Minnesota who lives with T1D herself, has used both Dexcom G6 and FreeStyle Libre and says there are different features that can be attractive to users depending on their needs and wants. She’s recapped her experiences using both in a blog post here.
For those who see a primary care doctor instead of an endocrinologist or diabetes specialist, Plunkett says it can often come down to that physician’s familiarity with CGM and diabetes technology in general. As a result, some PWDs may not get clear explanations or support in deciding on a particular device.
“What I’ve found with the FreeStyle Libre, it’s just so easy to slap it on your arm and you’re good to go,” she says. “The frustration with both systems will always be with the continuity of it reading your glucose. The last thing anyone wants is to be far from home on a run, and your CGM stops reading. It’s classic of both to drop you right when you don’t want them to. But the majority of the time, especially overnight, it’s so helpful to have a CGM on you to see what the trends are. The point is to help you make better decisions in your diabetes management.”
New York DCES Stahl, who often advises both inpatient and outpatient on CGM use, said, “Patients can get very frustrated and really lose confidence in the device when they see that the value is much different from a (fingerstick) blood glucose value..”
She added that “situations such as postprandial (post-meal) or during exercise in which glucose is changing rapidly, are especially prone to these discrepancies.”
Most often, Stahl and Plunkett say access and affordability are the biggest concerns for PWDs in considering a CGM. These insurance concerns often guide a person’s choice more than anything else, they say.
Both Dexcom G6 and FreeStyle Libre 2 present significant benefits for glucose management, but they each come with specific pros and cons that can influence user choice.
Dexcom G6 is considered to be the most accurate and comfortable full-featured CGM on the market, while FreeStyle Libre is a more “low-key tool” that offers fewer — and completely optional — alerts and alarms.
The mobile app capabilities and data-sharing with Dexcom G6 offer more options, and the “Urgent” alerts are particularly important for people who tend to experience frequent hypoglycemia, especially overnight.
While the FreeStyle Libre will eventually be integrated into automated systems with insulin pumps, that interoperability is currently an area where Dexcom G6 wins.
For many, access and affordability via insurance coverage remains the key factor in choosing a CGM — and FreeStyle Libre currently wins here with its lower price point.
As Plunkett puts it, “Insurance breaks hearts. Often, there’s no rhyme or reason (to coverage decisions) and that dictates what particular CGM someone can use, no matter what they may prefer. It would change the world of diabetes if everyone could get access to a CGM.”