Dexcom Vs. Medtronic Guardian Sensor - An Anecdotal Report

For the past week, Cat has been wearing both the Dexcom Continuous Glucose Monitor IN ADDITION TO her Medtronic Guardian 3 sensor that communicates with the Minimed 670g insulin pump.

Since she's doing the "run-in" phase of the pediatric clinical trial for the Tandem t:slim Control-IQ system, I decided to have her wear both and see how they compared. Fortunately, Cat is a good sport and didn't mind wearing two sensors to satisfy her mom's curiosity. 

First, let me backtrack and say that we have had basically no issues with the Medtronic 670g pump. Cat has been wearing hers since January 2018 and I have been wearing mine since January 2019. I am completely happy with the system. We have amazing time-in-range and few incidences of hypoglycemia, which are the new indicators for diabetes control as opposed to the older standard of A1C.

However, I'm not brand-loyal when it comes to insulin pumps and CGMS. Sorry not sorry! I'm always looking for the newest gadget and the latest and greatest in diabetes tech gear. So trialing the Control IQ sounded like a really cool idea! (For what it's worth, I requested to be in the next generation Medtronic 780 pump trials, but the closest trial location was too far for me to drive on a monthly basis). I've used the Omnipod, the first generation Tandem t:slim and now the Medtronic 670g, so I have good experience with insulin pumps. But I will jump on the first ship that sails when it comes to the best technology for managing Type 1 Diabetes!

So ANYWAY, like I said, Cat has been wearing both sensors for the last week. And in my opinion.....

MEDTRONIC GUARDIAN sensors were hands down the most accurate. I'm sure some people will disagree. However, how many naysayers have worn both sensors simultaneously? And I do have data to back this up!

Part of the trial requires that we use their Accu-chek meter to test Cat's BG. So sometimes I used the same drop of blood and checked her BG with both the Contour NextLink 2.4 meter (that is linked to her pump) and the Accu-chek, the clinical trial meter. BOTH meters were always within 5 points of each other when I tested with the SAME drop of blood, so I'd say they were both very accurate. However, when I compared the two meters with the Medtronic Guardian sensor and the Dexcom sensor, the Dexcom sometimes read 20-30 points higher than the two meters AND the Guardian sensor.

I will say there were times that the two sensors were spot on, especially early on. But it seemed like the later in the week that we got, the more the Dex was reading a little higher than everything else. But...who's to say that they Dexcom isn't right and the other three devices were wrong? I mean, there is a margin for error with meters as well. So there's that. I definitely didn't worry that the Dex was reading a little higher at times...it was not so off that I felt the need to calibrate it. And I would rather it trend higher rather than lower, too.

I'll provide some pics of the device comparisons below. Some are close and some are not so close. 

This one was on the first day of the Medtronic sensor. VERY close. I was extremely excited. 

These were a little off, but still within range of each other. NBD. 

Here they were all different, but still within 30% of each other so it was fine. 

This one was a little concerning...that's quite a difference! See how both meters basically matched the 670g but the Dex was 20-30 points higher? We saw this MULTIPLE times over the course of the week. Still within normal, but it was weird how Dex ran high more often than not.  

As far as which we liked the best, I'd say hands-down Cat prefers the Dexcom. The insertion is simple, the taping is simple, the no-finger pricks, no calibrations....MAJOR pluses. Also, the Dexcom G6 has a 10 day wear, opposed to a 7 day wear with the Medtronic sensor. (I've seen many complaints in the Diabetes Online Community about the G6 not lasting the full 10 days, and maybe it won't, but we are at the end of day 8 with no issues so far so I'll call that a win). 

I will have to say I love those features too. But this is week 2 with the Dexcom + Medtronic 670 and I am going to let her wear JUST the Dexcom. And the Dex doesn't talk to her pump. And that means we will lose the "suspend before low" feature in Manual Mode as well as the Auto Mode program which adjusts her basal. We've had really good success with Auto Mode keeping her in range, and I'm going to hate to have to micromanage her pump in order to do the same job. It will be hard! But, I'll deal with it for the sake of science and research for Type 1 diabetes!

And so for this week (week 2), we are NOT wearing a Guardian Sensor with the 670g pump,  and we are using the Dex for boluses without fingersticks or calibrations. Unless we need to fingerstick for whatever reason (her symptoms don't match the number on the Dex, or it's a first day sensor), then the Dexcom will be our guide. 

Next week (Friday) we will find out if we are in the control group for the t:slim (where we will wear the Dex and her medtronic 670 with no Guardian sensor, like we are doing this week), OR in the experimental group (wearing Dex + t:slim with Control IQ). 

I think it's obvious which one we are hoping for....stay tuned!