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What CGM systems are available in 2018?

Question:  what do Cerberus (the hound from hell), Chimera (the fire-breathing beast) and the backfield for the Super-Bowl-winning Phiadelphia Eagles have in common?

Answer:  All are 3-headed monsters capable of kicking some serious butt.

Why bring this up in a diabetes blog?  Simple.  The world of diabetes is chock full of 3-headed monsters.  We have three insulin makers, three dominant meter manufacturers, three pump companies, and for the first time, three companies producing CGMs (continuous glucose monitors).

Competition is definitely a good thing – it keeps all parties on their toes, striving to innovate, improve, and serve the customer in the best way possible while keeping costs down.  But having multiple options can make everything seem a bit more confusing.  There is no doubt that CGM can improve the quality of life and blood sugar control for just about everyone with diabetes.  But which system is best for you?

When making a choice, it helps to understand what each system has to offer:  the good, the bad, and the ugly (see – another threesome!).  We do our best here at Integrated Diabetes Services to remain fair & impartial when it comes to these types of comparisons.  We also try everything out personally before recommending anything to our patients.  So here are some facts and observations that might help you to become a more educated consumer.



Presently, personal-use, CGM systems are available from:

  1. Dexcom
  2. Abbott
  3. Medtronic

Dexcom’s system, called G5, will be replaced in the summer of 2018 by the G6 (don’t you love the creative names?).  G5 and G6 have many characteristics in common, but G6 offers a number of advantages, so we’ll discuss both.

Abbott’s system, called Freestyle Libre, was introduced in the US earlier this year, and has been available in other parts of the world (albeit a slightly different version) for the past several years.

And the latest entrant, Medtronic, is on the precipice of introducing the Guardian Connect system, a CGM that is not linked to a pump and can be used by just about anyone.


HEAD TO HEAD COMPARISON: The Latest Continuous Glucose Monitors


Dexcom is the system that most people are familiar with and has become somewhat synonymous with CGM.  The Dexcom G5 (to be replaced by the G6 in mid-2018) features a comfortable, easy-to-insert, long-lasting (approved for 7 days, most get about two weeks of use) sensor that produces the most accurate data in the CGM business.  Following a two-hour warmup period (during which data is not available) and initial fingerstick calibration, G5 asks for fingerstick calibrations at least once every 12 hours.  It continues to provide data even without the calibrations, but regular calibration is necessary to ensure ongoing accuracy.


The MARD (average difference between sensor values and lab values) is around 9%, and Dexcom clearly outperforms the other sensor in terms of accuracy when glucose levels are in a low range.  The re-usable transmitter emits a signal that carries approximately 20 feet, has a 3-month battery life and does not require any kind or charging or other maintenance.  The receiver displays the data (current glucose values updated every five minutes, trend graphs and rate-of-change arrows) and emits alerts (customizable beeps or vibrations) for pending high/low glucose values.  The high/low alerts can be customized by time-of-day.  The receiver can take the form of a handheld touch-screen receiver, a smart phone (iPhone or Android), or Tandem X2 insulin pump.  Those using a smart phone can have the data transmitted for viewing on a smart watch.  Because the data generated by G5 is stored in the cloud, loved ones have the option of seeing live reports on their cell phones and receiving alerts in the event of potential problems.

G5 transmitting to an iPhone

Dexcom’s recently approved G6 will offer everything G5 has to offer, plus a number of new benefits:  An even simpler 1-button insertion process, a flatter-profile sensor/transmitter, vastly improved day-1 accuracy, a 10-day sensor usage cycle (compared to the current 7-day cycle), a sensor that is unaffected by acetaminophen (Tylenol), and an optional predictive alert for very low glucose values.  The biggest improvement is that G6 is CALIBRATION-FREE.  No fingersticks are required.  Yet it achieves the same accuracy as G5 WITH calibrations.  Not bad!  However, G6 can accept calibration values in case the sensor is drifting off course and deviating significantly from fingerstick values.  The calibration entry allows the sensor to get back on track and improve its accuracy from that point forward.

Reports can be generated quickly and easily via Clarity software on either a PC or smartphone.  Data and reports can be shared automatically with healthcare providers in a variety of ways.  Dexcom is also compatible with just about every “midware” program (for merging data pump & CGM data), including Tidepool, Diasend and Glooko.


Freestyle Libre

Freestyle Libre has some but not all of the features of a traditional CGM.  The sensor and transmitter are combined into one compact unit that inserts very, very, very easily.  After a 12-hour warmup period, the user can “scan” the sensor with a handheld receiver to see a current glucose value along with a trend arrow and graph of the most recent eight hours of data.  The sensor/transmitter is replaced every 10 days (assuming the adhesive holds in place), and no re-use of sensors is possible.  NO fingerstick calibrations are required.  In fact, you CAN’T calibrate Libre, even if your fingersticks values differ by quite a bit from what the sensor is showing.

Libre is relatively inexpensive compared to other CGM systems (about $60 for the durable receiver/scanner, $40 per sensor).

Freestyle Libre sensor and reader

The accuracy of Libre is good despite the absence of fingerstick calibrations.  It has a MARD of about 10%, and the sensors are not affected by acetaminophen.  However, Libre is far less accurate when glucose levels are on the low side, producing false alerts (reading low when glucose isn’t really low) about 40% of the time.  And the inability to calibrate the system can sometimes leave the user with a sensor that runs chronically higher or lower than actual glucose values.

But the major drawback is the lack of alarms/alerts for pending high and low glucose levels.  The user has to physically “scan” the sensor in order to generate any data and see what is going on with their glucose level.  This can expose users to highs and lows any time they are not scanning, such as during the night, between meals, while driving, and when exercising.

Libre also lacks the ability to transmit data to a cell phone or to “share” the data electronically with loved ones and caregivers.  This will likely change over the next several years (there is even a company that is marketing a product to amplify the signal and send it to a smartphone), but for the time being, the only person who can see what’s going on is the one who is scanning the sensor.  Downloading is limited to Freestyle Libre desktop software, which does not merge data from other devices (such as pumps).  However, Libre and pump data can be merged through the Tidepool data management system.


Guardian Connect

The Guardian Connect system from Medtronic features the same Guardian sensor that is used with the Medtronic 670G hybrid closed-loop pump.  The sensor insertion process is relatively simple and painless, although the taping process can be clunky and cumbersome.  The transmitter uses Bluetooth technology to send signals to the Guardian Connect app that runs on various smartphones.  After a 2-hour warmup period, glucose readings are transmitted to the app every five minutes.  The sensor is intended for seven days of use, although many people find that they can re-use the same sensor beyond seven days.  However, as was the case with previous versions of Medtronic’s CGM, the transmitter must be removed from the sensor and re-charged on a weekly basis.


What’s really different now compared to prior Medtronic CGMs is the accuracy and reliability of the sensor.  When calibrated 3-4 times daily (using a really good meter, such as the Contour Next from Ascensia), its accuracy is close to that of Dexcom:  a MARD (average discrepancy between sensor and LAB values) of 9-10%.  The Guardian Connect App provides the user with high/low alerts that are customizable by time of day.  It also features predictive alerts that can help the user guard against highs and lows up to 60 minutes before they occur.  Although these types of long-term predictive alerts may generate some false alarms, they can also help users to spend more time within a safe target glucose range.

Another cool thing about Guardian Connect is… well… connectability.  Data from the app uploads automatically into Medtronic’s Carelink software.  This allows quick, easy access to a variety of reports by users as well as their healthcare providers.   Plus, loved ones can receive alerts via text message on their smartphones whenever trouble arises.  Medtronic has also developed a new feature for users:  Sugar IQ, a data analysis system that points out how everyday activities affect glucose levels.  Of course, this will require logging information into the app, and there’s no telling whether it will generate truly useful/applicable observations, but the prospect does sound interesting.

Dexcom G5/G6Freestyle LibreMedtronic Guardian Connect
MARD (lower number means better accuracy)9%10%10%
FDA Approved For agesAge 2+Age 18+Ages 14-75
Calibration Required?G5 – yes – 2x daily

G6 – NO, but can calibrate if sensor is off-track

No, and not possibleYes – 3-4xdaily
Sensor LifeG5: 7-14 days (or more)

G6: 10 days

10 days7 days
Warmup time

(New Sensor)

2 hours12 hours2 hours
TransmitterLasts 3 months, no rechargingFresh Transmitter connected to each sensorMust re-charge weekly
Display optionsSmart phone

smart watch (via phone BT connection),

Tandem X2 pump

Handheld receiver

Handheld scannerSmart phone

Smart watch (via phone connection)

Hi/Low AlertsYes, customizableNoneYes, customizable, including extended predictive alerts
Live Data SharingYes – high/low alerts and current glucose level/trendNoneYes – high/low alerts
Downloading/Data AnalysisAutomatic upload to Clarity software.

Compatible with most midware programs for merging data with other devices (Diasend, Glooko, Tidepool)

Freestyle Libre software

Tidepool (midware)

Automatic upload to Carelink Software

Sugar IQ program for analyzing data

Cost/CoverageApprox $300 per transmitter

$80 per sensor

$600 per receiver

G5 covered by Medicare and most private insurance plans

Approx $60 for scanner

$40 per sensor

Covered by Medicare and most private insurance plans

Approx $1000 per transmitter

$80 per sensor

Coverage Pending



Unlike choosing which of Cerberus’s heads is going to turn your head into its own personal lunch, choosing a CGM is really a no-lose proposition.  You will undoubtedly benefit from any system you choose.  However, as is the case with insulin pumps, certain ones may be a better choice for you personally.


DEXCOM G5/G6 is a great option for anyone who wants a reliable, proven system that is simple and flexible – particularly those who are treated with intensive insulin therapy.  The customizable high-low alerts and “sharing” features make it ideal for those trying to ward off serious hypoglycemia.  Although the sensors are a bit pricey, the ability to re-use them (until they stop working properly) helps keep the cost down.  Those looking to improve their diabetes management and spend more time within their target range can certainly benefit.  Dexcom is also in cahoots with a number of companies developing hybrid closed-loop systems, so use of Dexcom now creates a more seamless transition to future technologies.


FREESTYLE LIBRE is a nice choice for those who are at little risk of hypoglycemia, which includes most people with type-2 diabetes who are not taking insulin.  The prolonged warm-up period and lack of high/low alerts can leave the user vulnerable to dangerous glucose levels.  Also, the inability to calibrate the system may frustrate users who micro-manage their insulin and demand a high degree of accuracy.

It can also be a reasonable option for those who are easily distracted or annoyed by the alarms/alerts generated by the other CGM systems.  Finally, Libre is a good option for those who must pay out-of-pocket for their equipment and supplies.  The scanner costs a fraction of what the “hardware” costs with the other systems, and the sensors cost about half.


MEDTRONIC GUARDIAN CONNECT carries the Medtronic name, which means different thing to different people.  The company invests a ton in research & development, and is financially secure for the long-haul.  Medtronic puts a great deal of its resources into “what to do with the data.”  Their Carelink program and new Sugar IQ algorithm can be instrumental in helping users (and their clinicians) learn from the data and make therapeutic adjustments.  Technically-oriented users may enjoy these and other features of the Medtronic system.


Because out-of-pocket costs guide many of our health care decisions these days, it may be helpful to know that the Dexcom G5 and Freestyle Libre are covered by most private and public health insurance plans (including Medicare).  Medtronic and Dexcom G6 should be covered by most private plans, but not yet by Medicare.


To learn more about the various CGM options and determine which system best suits you, feel free to contact our office and schedule some time with one of our CGM-wearing CDEs.

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