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Continuous Glucose Monitors (CGMs)

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What They Do

Continuous glucose monitors (CGMs) measure the body’s glucose levels in real-time by sensing the glucose present in tissue fluid (also called interstitial fluid). Glucose is another word for sugar. Whereas a glucose meter provides a measurement of the blood glucose at a specific moment in time (fingerstick), CGMs typically provide a new glucose level every five minutes, meaning 288 times per day. An apt analogy is that a meter is similar to a photo – providing a single blood sugar “snap shot” – while a CGM is like a video, providing a constant stream of information on glucose levels, trends, and overnight data. CGMs provide a good way to monitor time spent “in range” (time spent within a normal, pre-specified blood sugar range), and can warn users if they are trending towards hypo or hyperglycemia. For more on time-in-range goals, see here and here. CGMs are particularly useful after meals and overnight, as they can sound an alert when glucose levels drop or rise below a preset threshold. Some CGMs need to be calibrated with a fingerstick blood sugar reading for optimal sensor accuracy; two CGMs currently do not need fingerstick calibrations – Abbott's FreeStyle Libre and the Dexcom G6.  

What Supplies Do I Need?

CGMs require three basic parts:

  • Sensor – monitors real-time glucose levels, usually every five minutes. The sensor is inserted under the skin by the user with a simple applicator. Sensors are normally worn for 7-14 days, depending on the system.

  • Transmitter – sits on top of the sensor and sends glucose information to the receiver/app. Most systems have a transmitter that is reusable for 3-12 months. In the case of FreeStyle Libre, there is no reusable transmitter; each sensor is fully disposed after 14 days and a new one is put on.

  • Smartphone app, receiver, and/or pump – displays real-time glucose number, trend, and history. Most current CGMs offer smartphone apps for viewing data. Abbott and Dexcom also offer handheld devices for those that don’t/can’t use a smartphone. Some CGM devices also send the glucose value to an insulin pump, including a growing number that can automate insulin delivery accordingly.

What CGMs are available in the US?

Last updated: November 27, 2018

Currently, four companies have personal CGM devices on the US market: Abbott (FreeStyle Libre), Dexcom (G4, G5, G6), Medtronic (Guardian Connect and Guardian Sensor 3), and Senseonics Eversense. The table below compares some of their key features. Pricing varies with insurance coverage and can be provided by the company. For those paying cash (no insurance coverage), FreeStyle Libre is the least expensive device as of this writing.


FreeStyle Libre 14-Day (US)

Dexcom G6

Medtronic Guardian Sensor 3
(670G, Guardian Connect)

Senseonics Eversense (US)

Fingerstick Calibration

0 - Factory Calibrated

0 - Factory Calibrated

2/day minimum

2/day minimum


Replaces fingersticks for treatment decisions

Replaces fingersticks for treatment decisions

Requires fingerstick confirmation

Requires fingerstick confirmation


18+ years

2+ Years

7+ Years (670G)

14+ Years (Guardian Connect)

18+ Years

Medicare coverage






1 hour

2 Hours

2 Hours

24 hours after implantation

Wear length

14 Days

10 Days

7 Days

90 Days

Alarms for Lows, Highs

None in US – must scan sensor to see glucose, eight-hour history stored on sensor patch




Data display

Reader device or iPhone app (FreeStyle Libre Link)

Receiver, Android and iPhone apps, smartwatches, Tandem t:slim X2 pump

670G pump only


Guardian Connect app only on iPhone

Android and iPhone apps

Transmitter design and on-body form factor

~2 stacked quarters, one-press insertion

Fully disposable transmitter integrated with sensor patch

Small eraser sized transmitter, one-button inserter

Three-month use transmitter separate from sensor

~2 stacked quarters (clamshell), inserter device

Rechargeable transmitter separate from sensor

Watchface-sized transmitter. Sensor is inserted by a healthcare provider via in-office procedure

Rechargeable transmitter separate from sensor

Useful Links:

Abbott FreeStyle Libre

Abbott FreeStyle Libre 14-Day Obtains Medicare Coverage – Covered for people on intensive insulin therapy (multiple daily injections or insulin pump) – this includes both type 1 and type 2 diabetes.

FreeStyle Libre in US Now Approved for 14-Day Wear and 1-Hour Warmup – Approved for adults, the latest FreeStyle Libre features a longer wear time and shorter calibration than the original 10-day version.

LibreLinkUp App Launches in Europe, Enabling Remote Monitoring of FreeStyle Libre Sensor Readings – Following a wearer’s scan of the FreeStyle Libre sensor with their own LibreLink Android app, a caregiver will immediately be able to see the result and receive high or low glucose notifications in LibreLinkUp.


Dexcom G6 CGM: No Fingersticks, One-Button Insertion, and 10-Day Wear – What’s great about Dexcom’s G6, what could be even better, and how the new CGM compares to the G5.

Dexcom G6 Obtains Medicare Coverage – Covered for people on intensive insulin therapy (multiple daily injections or insulin pump) – this includes both type 1 and type 2 diabetes.


What’s next for Medtronic Diabetes? A Look into CGM and Pump Pipeline – Medtronic hopes to launch at least 10 products over the next two years – including a new CGM and apps!


FDA Approves Senseonics’ Eversense 90-Day Implantable CGM, On-Body Transmitter, and Smartphone Apps – The system includes a pill-sized sensor implanted in the upper arm for 90 days, an on-body transmitter, and a smartphone app for viewing data (Apple, Android). Eversense’s 90-day wear removes the need for frequent sensor insertions required by other CGMs. The 180-day wear Eversense XL version has already been approved in Europe.

Other CGM Links

Understanding Average Glucose, Standard Deviation, CV, and Blood Sugar Variability – What do these numbers mean, what’s the target, and how can they provide insight into better diabetes management? Example days included!

Time-in-Range: What’s an Achievable Goal with Diabetes? Adam's approach to time-in-range goals, five key tips to spend more time-in-range each day, and what’s still to come from experts…

CGM and Time-in-Range: What Do Diabetes Experts Think About Goals? We interviewed 15 experts about time-in-range goals for those wearing CGM. Here’s what they said…

CGM Can Help People with Type 2 Diabetes on Injections – Individuals with type 2 diabetes show A1C and time-in-range improvements when using CGM.

CGM Tips and Tricks for Better Accuracy and Less FrustrationAdam shares what he has learned from 50,000 hours using CGM.

Beyond the Numbers: Continuous Monitors Offer Much More Than Blood Glucose Readings – Gary Scheiner (M.S., CDE) explains the benefits that CGM bring over standard blood glucose meters.

Remote Monitoring of CGM Data

Remote monitoring allows for a person’s blood glucose numbers or CGM data to be shared with others. While several meters allow for data uploading, remote monitoring is now available for many CGM devices. Remote monitoring can give peace of mind to loved ones. For example, a traveling spouse could share their CGM data with family at home, a child at a sleepover could share with his/her parents, or a patient can send updates directly to a health care provider.

“Can I Follow Your CGM?” Having a Conversation About Sharing Your Data Learn more about the decision to share your CGM data.

Nightscout Bringing CGM to the Cloud – SixUntilMe Blogger Kerri Sparling gives an overview of the what, why, and how of the Nightscout project and CGM remote monitoring.

Please note, this page is not a comprehensive list of all of the available resources or products available. All links are organized chronologically within their respective sections.