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March 10, 2020

Continuous Sensing, Insulin Pumps

Question from Superior, Wisconsin, USA:

My daughter has finally decided to give the CGM a try and the Dexcom was recommended. My daughter uses a Medtronic 670G insulin pump and I understand there is a Medtronic CGM that will communicate with this pump to automatically adjust insulin dose based upon the CGM reading. It’s also my understanding that the Dexcom would not provide this feature. Can you please give me more information on why the Dexcom would have been recommended over the Medtronic? Is it because of the calibration effort needed with the Medtronic? Any additional information you can provide would be helpful.


From: Gary Scheiner, MS, CDCES

You ask an excellent question. There is certainly a benefit to using a CGM that links with a pump and insulin-adjustment algorithm (collectively called a “hybrid closed loop system”). The 670G can raise/lower basal insulin automatically based on the sensor’s glucose trends. This can produce more time in-range (typically around 70 to 75%), minimal hypoglycemia, and a pretty good overall average (around 130 to 150) when it is used properly and consistently.

However, there is a price to pay when using the sensor that works with the 670G (called the Guardian 3 sensor). Compared to the Dexcom G6, the Guardian 3 is somewhat less accurate, requires a much more complex insertion and taping process, uses a transmitter that must be recharged every 7 days (Dexcom’s transmitter does not require any recharging), a sensor that must be changed every 7 days (Dexcom’s lasts 10 days), no “sharing” capability with loved ones (Dexcom G6 data can easily be tracked and produce alerts on loved ones’ smart phones), occasional lost signals (Dexcom’s bluetooth communication is cleaner that Medtronic’s radio signals) and calibration at least twice daily (Dexcom requires none).

When weighing the benefit of the hybrid closed loop adjustments against the quality of the Dexcom G6, you might consider where you are coming from. If your daughter’s control is pretty good already, you would probably not benefit enough from the hybrid closed loop to make use of Medtronic’s sensor worthwhile. However, if her control is very poor, or she is plagued by frequent/severe hypoglycemia, using the Medtronic hybrid closed loop may provide enough benefit to make use of their sensor worthwhile.

Editor's Comments:

If you choose to use a Dexcom G6, there are two other insulin delivery devices that use the G6, should you want to change pumps in the future. The Tandem Control IQ technology automatically adjusts insulin levels based on Dexcom G6 continuous glucose monitoring (CGM) readings. And, the Omnipod Horizon, which is currently in clinical trials, is an automated insulin delivery (AID) system that uses continuous glucose monitor (CGM) readings to automatically adjust basal insulin delivery. Insulet Corporation hopes to have the Horizon work with the G6, G7 (in the future), and Abbott’s FreeStyle Libre 2. Gary Scheiner has previously reviewed the CGMs currently on the market at Continuous Glucose Monitor Comparisons and Reviews.