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Comparison of Continuous Glucose Monitors.

Comparison of Continuous Glucose Monitors

The world of glucose monitoring is making an exciting shift from sole reliance on blood glucose meters to the increasing use of continuous glucose monitors. Continuous glucose monitors (CGM) provide glucose levels continuously (every 1 to 5 minutes) throughout the day by measuring glucose levels in the interstitial fluid (fluid between the body cells). Having such information allows the user to be proactive by seeing, in real-time, how food, exercise, and medication impact glucose levels.

Since their entry into the market place in 2000, continuous glucose monitors have continually been innovated resulting in improved accuracy, smaller sensors, and transmitters, and longer length of wear.1  In addition, insurance coverage for these devices continues to expand and improve making them more affordable. Research has shown that consistent use of CGM technology reduces hypoglycemia, lessens glycemic variability, and improves A1c.2

This article will compare many of the features available with the newest CGMs. For more background information on CGMs please refer to this article:

Medtronic Guardian Connect

Parts of the system: Guardian 3 sensor, Guardian 3 transmitter, Guardian connect app (displays sensor glucose data on smart phone), one-press serter – device used for placement of sensor

Sensor wear duration: 7 days

Sensor placement: Back of upper arm, abdomen (2 inches away from navel)

Warm-up time: Up to 2 hours

Alerts: Predictive alerts (notifies user of impending low glucose or high glucose) and threshold Alerts (notifies user of high glucose and low glucose)

Data Sharing: Yes, via a web-based app “care-partners” can receive text message alerts3

Accuracy: MARD (see below for definition): 8.7% when placed on the arm and calibrated 3-4 times/day and 9.6% when placed on abdomen and calibrated 3-4 times/day3

Dosing decisions: No. All dosing decisions require a blood glucose confirmation

Calibration (see below for definition): Every 12 hours3,4

Dexcom G 6

Parts of the system: Sensor, transmitter, display device (App on phone or Receiver), auto-applicator – device used for placement of sensor

Sensor wear duration: 10 days

Sensor placement: Abdomen (2 inches away from naval)

Warm-up time: 2 hours

Alerts: Urgent Low Soon Alert (20 minute warning prior to reaching or going below a glucose of 55 mg/dL) and threshold alerts (notifies user of high glucose and low glucose)

Data sharing: Yes, via the Dexcom Share App. Users can invite up to 5 people to followers to view real-time data and program text message alerts.

Accuracy: MARD: 9% 

Dosing decisions: Yes

Calibration: None required5

Freestyle Libre

Parts of the system: Sensor and reader, sensor applicator (device used for placement of sensor) and reader can also be used as a blood glucose monitor

Sensor wear duration: 10 days

Sensor placement: Back of upper arm

Warm-up time: 12 hours

Alerts: No alerts unless the sensor is scanned by Reader

Data sharing: No

Accuracy: MARD: 9.7 %6

Dosing Decisions: Yes

Calibration: None required


MARD: Mean Absolute Relative Difference is a statistical measure of accuracy; the lower the number, the better.5

Calibration: Blood glucose readings entered into the CGM system to help ensure the sensor glucose readings remain accurate over time.7

Do you currently use a continuous glucose monitor? Please share your experience with the community.

This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

  1. lczuk D, Priefer R. A history of continuous glucose monitors (CGMs) in self-monitoring of diabetes mellitus. Diabetes & Metabolic Syndrome. 2018; 12(2): 181-187.
  2. Klonoff D, Ahn D, Drincic A. Continuous glucose monitoring: A review of the technology and clinical use. Diabetes Research and Clinical Practice. 2017; 133: 178-192.
  3. MiniMed 670G Insulin Pump System. Medtronic. Published 2018. Accessed April 30, 2018.
  4. Help your patients outsmart diabetes. NEW! The Guardian™ Connect CGM System. The only standalone Smart CGM system. Medtronic. Published 2018. Accessed April 30, 2018.
  5. Dexcom Products. Personal CGM. The Dexcom G6 Continuous Glucose Monitoring (CGM) System. Dexcom. Published 2018. Access April 30, 2018.
  6. Discover the Freestyle Libre system. Freestyle Libre. Published September 2017. Accessed April 30, 2018.
  7. Sensors and Transmitters. Medtronic. Accessed April 30, 2018.


  • goat66
    5 months ago

    I also , as type 2 40 years use Freestyle 14 day sensor. It helps. I get better % in target of 70 to 180 with use of both Longlasting and a mealtime fast insulin than I get in use of an example like a 70/30 mixed insulin. But I also require more shots per day. I hope, as type two, to try either 24 hour fast, or continue reduced carb and calorie meals to drop some weight, lowering meds same time.

  • Kelly Dabel, RD moderator
    5 months ago

    Thanks for sharing! Glad that you’ve found it helpful in the management of your numbers. We appreciate you sharing your experience. Wishing you the best, Kelly, Community Moderator

  • goat66
    10 months ago

    freestyle libre now has a 14 day sensor and reader, warm up time of only one hour, so its a new CGM system, but already offers a bit of improvement to user. Cost is climbing, but as a 40 year T2 I find it to be helpful. It gives average BS 7, 14, 30, and 90 days, and an item called in target BS. My own time in 70 to 180 is 92%.

  • Shelley, TheLongPointGirl moderator
    10 months ago

    I got my first sensor 8 days ago. So far, I love it.

  • goat66
    10 months ago

    Hi. I been T 2 40 years, used the little kit and finger sticks to check blood sugar, one or two a day in early years, 3 to 5 sticks in last near decade… I have only used CGM for 1 past year, abbott freestyple libre style. CGM is not low cost and some, or many insurance plans will not help pay for it. I am now on medicare and they help pay this cost but as I understand its only for 3 to 5 finger sticks and 3+ insulin shots /da. people on more than long term insulin 1/da.

  • Kelly Dabel, RD moderator
    10 months ago

    Thank you so much for sharing your story and experience! So glad that using a CGM has been helpful to you. We appreciate you sharing the pros and cons. Best, Kelly, Community Moderator

  • T2Dquestions
    10 months ago

    Hi all….question here… a lot of T2D’s use CGM’s? My doctor has not mentioned it to me as an option. Curious if it helped and what kind you use and why. Thank you!! 🙂

  • Kelly Dabel, RD moderator
    10 months ago

    Thanks for reaching out! I would say that there is a relatively small percentage of people with Type 2 Diabetes using CGMs. They are more commonly seen in those with Type 1 or for those with particularly brittle control. CGMs can be especially useful for people who are less aware of changes in blood glucose or have a difficult time remembering to do regular monitoring. If your glucose level decreases or increases over a pre-set level, the monitor can alert you with an alarm. This can be particularly helpful in people who require intensive insulin therapy. The monitors can be used in conjunction with an insulin pump. It doesn’t hurt to speak with your doctor about it and get their feedback as to whether a CGM may be useful to you. Best, Kelly, Community Moderator

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