A continuous glucose monitor or CGM reveals short-term trends in glucose as they happen. You can see the direction your glucose has taken over the last 1, 3, 6, 9, 12, or 24 hours. Upload your data to view reports of averages and trends over periods of up to 90 days.
CGMs are now widespread and widely covered by insurance to benefit both Type 1s and Type 2s. Several manufacturers are getting in on the action, offering a variety of features and costs.
Major players in the field include Dexcom, Medtronic, Freestyle Libre, and Eversense. We discuss the features of each below.
Dexcom was one of the first developers of CGM technology. Their latest, the Dexcom G6, makes monitoring your glucose easy. Each sensor lasts 10 days. While they are only FDA-approved for placement on the stomach, many users report successfully wearing them on arms and even legs with little or no loss of accuracy. This provides for more flexible arrangements, especially if you also wear a pump.
Arguably the leader in CGMs, the Dexcom G6 integrates with the Tandem t:slim pump with its Control-IQ automated insulin delivery technology.
Sensors last 10 days, but resourceful users concerned about keeping costs say they can extend their use. Katie DiSimone has tips on how to extend their use. This is for the brave of heart, and we have not confirmed their optimism.
Each sensor comes pre-loaded in a single-use applicator that applies the sensor to the skin, making insertion easy. A reusable transmitter then snaps into the sensor. Although the G6 does not require an over-tape, Dexcom offers one that many pumpers use. The transmitter requires no charging and gets replaced every 90 days. The cost is $199 for those without insurance.
The G6 requires no calibration, but you can calibrate if a meter reading differs from that of the CGM. Dexcom earned its no-calibration designation from the FDA because of its consistent accuracy over 10 days.
The G6 works with a dedicated receiver, an insulin pump (Tandem t:slim or Omnipod), or an app on your smartphone. A smartwatch can display glucose readings for quick viewing.
With the Clarity app, the G6 automatically loads data to it, and from which you can later generate reports for yourself or your healthcare team.
Dexcom’s progress on the Dexcom G7 appears to be well underway. The G7 combines the sensor and transmitter into a single unit that gets replaced every 10 and perhaps every 14 days. We expect it to improve accuracy and have a slimmer profile, a smaller application device, and lower cost. Dexcom is working to launch the G7 by the end of 2021 and hopes to have cell phone connectivity early in 2022. Following Abbott’s model, Dexcom plans to distribute the G7 CGM directly in pharmacies for customer convenience.
The standalone connects to your smartphone to view readings—there is no available receiver. For the 670G hybrid-closed-loop system, readings are viewable on the insulin pump’s screen.
Both use the same sensors, just with different transmitters. Sensors need to be changed every 7 days. Given that, Guardian users have figured out how to extend sensor use and reduce out-of-pocket expenses.
The transmitter is a small clamshell-shaped smooth plastic with a more rounded and slightly lower profile than the Dexcom. It comes with a separate over-tape to hold it in place.
Guardian 3 does not have FDA’s designation for accuracy sufficient to make dosing decisions, so it requires at least two daily finger-stick calibrations. It is FDA-approved for wear on the stomach or back of the arm.
Medtronic’s Guardian 4 sensor has already received CE approval in Europe, requires calibrations (no finger-sticks), and readings are directly used for bolus calculations. It works with the new 780G insulin pump, as well as the InPen smartpen phone app and bolus calculator.
On its own, the Freestyle Libre 2 is not yet a true CGM. You must scan with the reader or smartphone over the sensor to get readings. However, vibration or sound is available to warn when you are out of your target range, so you know when to scan. The Freestyle Libre and now the Libre 2 from Abbott remain a popular lower-cost option for many. With 14-day sensor wear and no finger-stick calibrations required, it is simple and easy to use.
You can scan with either a separate reader or with your smartphone that has the LibreLink app. The LibreLinkup app allows sharing with up to 20 users.
A popular third-party solution turns Libre 2s into a real-time continuous glucose monitor by adding a Blucon NightRider from Ambrosia Systems. When the NightRider is clipped on top of the Libre, it provides real-time alerts via a smartphone app. The Libre 2/NightRider combo reduces out-of-pocket expenses to about a third that of other CGM systems.
Abbott is in rapid transition, with its Freestyle Libre 3 CGM now having CE approval in Europe for 14-day wear. The Libre 3 sports the smallest CGM size, a one-piece applicator, glucose readings on your cell phone, and no requirement for finger-stick calibrations. The Libre 3 is ideal for those on multiple injections, with integration into the insulin pump a possibility.
Eversense from Senseonics is the only implantable sensor. A small capsule-shaped sensor is inserted under the skin of the back of the upper arm. This requires a visit to your doctor’s office every 90 days to switch the sensor out. An external transmitter is placed over it, attached with adhesive to the skin. This can be temporarily removed, such as swimming or a formal event.
It’s a good thing it’s removable because the transmitter requires daily (or sometimes more often) charging. Eversense requires twice-daily finger-stick calibration. But, at 90 days, it’s the longest-lasting sensor and offers a certain flexibility and freedom. It’s also the only CGM to provide on-body vibration alerts for low or high glucose levels, even if your smartphone isn’t with you.
Eversense has applied to the FDA for 180-day wear, and we believe is working on a no-calibration status.
Our Continuous Glucose Monitor Comparison
|Days of Sensor Wear
|Integration with pump
|Tandem t:slim Control-IQ (and older Basal-IQ)
|Yes and No:
The Guardian 3 is part of the 670g hybrid closed-loop insulin pump system.
The Guardian Connect is a standalone CGM that does not connect to any pump.
|Transmitter: $300 every 90 days
Sensors: $420 for 30 day supply
Receiver (not necessary if using smartphone): $380 one time purchase
|Rechargeable Transmitter: $1100 (1 year warranty, may last longer)
Sensors: $450 for box of 5 (35 day supply)
|Sensors: $135 for 28 day supply
Reader (not necessary if using smartphone): $175
|$1400 for sensor, transmitter, and supplies, plus cost of insertion in doctor’s office.
Limited time Eversense Bridge program limits the cost to $99 plus insertion
|Android, iOs, Apple Watch
|Android, iOs, Apple Watch
|Up to 10 people with Dexcom Follow app (Apple, Google)
|Up to 4 people with CareLink™ Connect web app (Apple, Google)
|Up to 20 people with LibreLinkup app (Apple, Google)
|Up to 5 people with Eversense Now app
|Separate Receiver available
|8 feet for up to 24 hours
|7.5 feet for 10 minutes
|3 feet or for 30 minutes
|1 meter (about 3 feet) for 30 minutes