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 different manufacturers are getting in on the action, and have varying features and costs.
The major players in the field are Dexcom, Medtronic, Freestyle Libre, and Eversense. Discussed below are the features of each.
Dexcom was one of the first developers of CGM technology. Their latest, the Dexcom G6, makes monitoring your glucose easy. The sensors last 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.
The sensors are applied to the skin using a one-time-use inserter that makes insertion easy. The reusable transmitter is then snapped into the sensor. No over-tape is required, but Dexcom has one that can be added. The transmitter requires no charging and can be used for 90 days before they must be replaced for $199 for those without insurance.
The G6 requires no calibration, and this is generally not required. However, the system does allow calibration if errant readings are encountered. Dexcom earned its no-calibration designation from the FDA due to 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. Readings can also be viewed on a smartwatch, as long as the phone is nearby.
Data can be loaded into the Clarity app to generate reports for you and your healthcare team.
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, wearers of the Guardian have figured out how to extend the sensor to 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 at least two daily fingerstick calibrations are required and recommended. It is FDA approved to wear either on the stomach or back of the arm.
By itself, the Freestyle Libre 2 is not yet a true CGM. You still have to physically scan your reader or smartphone over the sensor to get readings. However, it adds vibration or sound 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 fingerstick 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 that turns old Libres and new Libre 2s into a real-time continuous glucose monitor comes by adding a Blucon NightRider from Ambrosia Systems. The NightRider sits right on top of the Libre to provide real-time alerts via a smartphone app. With the Libre 2/NightRider combo, out of pocket expenses are about a third or less that of the other CGM systems.
Eversense from Senseonics is the only implantable sensor. A small capsule-shaped sensor is implanted via an incision under the skin of the back of the upper arm–a visit to the doctor’s office every 90 days is required to switch the sensor out. An external transmitter is worn over it, attached with adhesive to the skin. This offers the option of removing it when you don’t want to have something on your arm, 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 also requires twice-daily fingerstick 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.
Our Continuous Glucose Monitor Comparison
|Dexcom G6||Guardian 3||Libre 2||Eversense|
|Days of Sensor Wear||10||7||14||90|
|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.
|Cost||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
|Smartphone integration||Android, iOs, Apple Watch||Android, iOs||Android, iOs||Android, iOs, Apple Watch|
|Data sharing||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||Yes||No||Yes||No|
|Water Resistance||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|