Which CGM is the best? At DiabetesLab, we analyzed your opinions, and here is a summary.
Accuracy of different systems
CGM accuracy is measured as MARD (mean absolute relative difference between CGM readings and blood glucose readings). This is an error metric – lower MARD is better.
Dexcom 505 AP (USA)
|9% officially 1|
|Dexcom G4 original algorithm||13.00% officially 2
12.60% in the test by IDS
|Medtronic Enlite||13.60% officially 3
18.66% in a test by IDS
|Abbott Freestyle Navigator 2||11% officially|
|Abbott Freestyle Libre||11,4% 4|
1 J Diabetes Sci Technol. 2015 Mar;9(2):209-14. doi: 10.1177/1932296814559746. Epub 2014 Nov 3.
2 Diabetes Technol Ther. 2013 Oct;15(10):881-8. doi: 10.1089/dia.2013.0077. Epub 2013 Jun 18.
3 Diabetes Technol Ther. 2014 May;16(5):277-83. doi: 10.1089/dia.2013.0222. Epub 2014 Apr 7.
4 Diabetes Technol Ther. 2015 Nov;17(11):787-94. doi: 10.1089/dia.2014.0378. Epub 2015 Jul 14.
Dexcom G4 and G5
With the latest algorithm update, Dexcom became the most accurate CGM system on the market. FDA-approved sensor life is 7 days, but most people would restart sensor when it expires it tends to track accurately on the 2nd and 3rd week.The most recent version of the system, Dexcom G5, is already shipping in the Unites States and the United Kingdom. There is a new app Dexcom Clarity which spots glucose insights. G5 has features such as displaying CGM data directly on a smartphone, without having to keep a Dexcom receiver around. Data can be transmitted to iOS devices and Apple watches (USA) or a variety of other devices worldwide thanks to Nightscout‘s do-it-yourself projects. There are still things to tweak in G5; here is a review.
Current versions available on the market:
- Dexcom G4 Platinum, a classic stand-alone system, which is the most recent one available in Europe and does not include 505 AP algorithm update. It doesn’t communicate with smartphones.
- Dexcom G4 transmitting data to Animas’ Vibe insulin pumps. You don’t need a separate receiver – CGM data is shown on the pump screen. The algorithm is hardcoded into the pump and doesn’t include the latest update. No smartphone communication.
- 505 “Artificial Pancreas” software update for Dexcom G4 released in 2014 in the United States – improved accuracy.
- New Dexcom G4 with Share receivers available in the US. These receivers already work with the 505 algorithm and can transmit data to a smartphone.
- Tandem t:slim insulin pump integrated with Dexcom G4 (US only).
- Dexcom G5 with all the latest updates – already on the market in the US and is about to appear in Europe.
Medtronic sells CGM sensors which connect to their insulin pumps. Stand-alone devices are also available. Medtronic sensors are statistically less accurate than Dexcom (MARD 13.6%), which can be frustrating for some users. Approved sensor life is 6 days; in practice people would restart it, to make 10-12 days out of sensor life.
- not so accurate;
- uncomfortable to wear;
- there are happy users, though!
Facebook screenshots with examples of users’ feedback:
This CGM is easier to try for Medtronic pump users: the initial costs will be lower, because the data is shown on the screen of the pump you already have. With a recently launched Bluetooth device MiniMed Connect ($199), pump and CGM data can be transmitted to a smartphone app, for now iOS only, and US only.
Abbott Freestyle Navigator II
Abbott Freestyle Navigator II is available only in specific countries, such as UK, Netherlands, Israel. It is not planned to be available in the United States. Navigator was the most accurate CGM in the world before the launch of Dexcom’s 505 algorithm.
It provides a new glucose reading every minute, as opposed to 5 minutes for Dexcom. Approved sensor life is 5 days, but it may last longer. Navigator requires only 5 calibrations in 5 days, at increasing intervals, using a built-in glucometer. Occasionally the system may ask for additional calibration in case of unstable glucose levels.
There are predictive alarms based on glucose trends.
“My No. 1 problem with the sensor is the adhesive performance, or lack thereof. [solved by using a wipe and a Flexifix tape] “I also had a problem with a couple of faulty sensor inserters that didn’t release the sensor into the skin.”
“I have found the Nav2 CGM readings to be quite accurate, typically within 10% of the FreeStyle glucometer results. I have done some random tests to compare, and can say non-scientifically that I am very happy with the system’s accuracy.”
“Here in Israel I have full, literally 100% reimbursement so I haven’t had to extend the sensor life to save cash. As to cost, I asked last year and it was something like $2,000 for the device and $600 monthly for the consumables.”
Libre is in clinical trials in the United States and is available in certain countries in Europe. There are problems with its availability because of low manufacturing capacity.
It’s “flash glucose monitoring”, not real-time monitoring: you need to manually slide the device past the sensor to receive the latest data. No alarms — because information is not continuously transmitted from the sensor to the device. So we cannot call it a real CGM. Abbott markets the device as something in between CGM and fingersticks.
Libre doesn’t require a separate transmitter — everything is integrated into the sensor. Sensor is placed on forearm; device communicates with the sensor via NFC. Sensor stores up to 8 hours of information. You need to slide the device past the sensor at least once in 8 hours to save a complete picture of glucose. To save storage, Freestyle Libre keeps only one glucose reading for each 15 minutes, even though it takes measurements each minute.
Libre doesn’t need calibration — because it’s “factory-calibrated”. You can’t do anything with bad sensors, since you cannot calibrate them. Libre uses predictive algorithms to minimize delay with interstitial fluid. Then rewrites history if it was wrong.
“in many cases, the Libre predicts what your BG should be by projecting itself in the future. Sometimes, it gets it wrong, especially when for example it sees a constant increase and you start to exercise.” (Pierre)
Likely to use an algorithm to compensate for the temperature.
“Smaller, less painful sensor than traditional CGM. Very simple insertion process, does not require training. FreeStyle Libre is approved for dosing insulin except in three cases: when hypoglycemic, when glucose is changing rapidly, or when symptoms don’t match the system’s readings.” (DiaTribe review)
There is an option to use Libre as a traditional glucose meter – with Freestyle Optium test strips for blood glucose and blood ketones.
Libre also has a hidden bolus calculator, which is supposed to be set up by a healthcare professional, and it can be activated by entering a special code.
CGM graph on the screen is not so detailed, you cannot zoom it.
“It seems to me that the Libre has been designed around the needs of multiple injection people rather than pumpers who are more likely to be using “sugar surfing” techniques” (Facebook)
Libre is not approved for driving in the UK:
“Police & DVLA won’t accept readings from the Libre, you can be asked to show your BG meter if stopped.” (Facebook)
Libre readers are targeted at each specific country: units (mg/dL or mmol/L) are hardcoded in the reader. The same with the language. Currently you can buy an English version only with mmol/L (UK market).
A Libre sensor lasts for 14 days (hardcoded). The sensor cannot be restarted as a new one. The first 1-2 days are normally less accurate. It helps to insert the sensor 1 day before, so that the sensor starts tracking more accurately from the beginning.
Abbott put a lot of work on visualization techniques. Example of a “typical day” report:
Experience with different systems
Simultaneous run of Libre and Dexcom G4:
The sensors weren’t perfect: the Libre missed a single clinical, meter confirmed, low on the third day. The Dexcom had several misses that we found extremely annoying. For example, the Dexcom missed a bad low on day 12. We wouldn’t run a totally automated artificial pancreas that aims for our level of control on either sensor alone.
— “14 days with the Dexcom G4 (non AP) and the Freestyle Libre” by Pierre Vandevenne
Difference between accuracy of Dexcom, xDrip and Libre is largely explained by the difference in the algorithms (not only the sensor technology).
“To put it bluntly, once you have used well behaved Libre sensors, it is extremely hard to remain satisfied with the performance of the G4 non-AP system. Our initial tests seem to show that [xDrip] performance is closer to a good Libre sensor (and to the 505 AP Dexcom algorithm should be) than the standard G4 non AP system. [..] I suspect it will be somewhat constrained in terms of speed by the sparse 5 min Dexcom sampling, but we’ll see.“
— Abbott Libre Update by Pierre Vandevenne
Time lag of Dexcom (in comparison with blood glucose readings) is larger than time lag of Libre. Still both sensors are not too reliable in case of rapidly changing levels:
The only times when [Libre] has been wildly out has been when I have had a faulty sensor (which Abbott replaced free of charge) or when my blood sugar has been rapidly changing and this has been visible from the trending arrows. Sometimes there are gaps in the Freestyle Libre data, this appears to be when my blood sugar has changed very rapidly.
The only time I found the Dexcom to be inaccurate was when I became frustrated and tried to overly calibrate it. However once I left it to work itself out and have stuck to 12 hour calibrations the accuracy is great.
From the point of view of accuracy, device connectivity and ecosystem, our winner is Dexcom. The decision is always yours — you may want to consider factors such as insurance coverage, out-of-pocket costs, or availability of specific devices in your country. A promising runner-up is Freestyle Libre which is more discrete to wear and doesn’t require calibrations, but doesn’t have all benefits of Dexcom yet.
Products coming soon
- Senseonics Eversense, an implanted CGM that lasts 90 days. The system consists of an implantable sensor, an external transmitter, and a smartphone app. Exceptional results in a clinical trial: 8.8% MARD, better than any CGM on the market. Eversense is already available in Sweden and Germany, and scheduled to launch in other countries of Europe and Middle East.
- Medtrum is a tubeless artificial pancreas initiative from China. They have a disposable CGM system, EasySense. Reported accuracy is at the level of Dexcom G5 (MARD around 9%). The company announced a distributor in the UK.
- SugarBeat CGM system, with a daily-disposable adhesive skin-patch, has been approved in Europe. Its launch is planned for 2017.
- Dexcom G6 may be available in 2017.
- Medtronic developed a new more accurate sensor, Guardian 3, with reported MARD of 10.55%. Recently approved Medtronic’s MiniMed 670G pump (to be launched in Spring 2017) will use this sensor.
Last updated: 22 January 2017