Just started on 670G: Dueling CGM Throwdown!

As of Monday this week, (8/29/17) I started on the 670G and as a result switched to the Guardian 3 CGM system–my biggest misgiving about the whole deal. Thing is, I already had a Dexcom G5 session going, so rather than pulling the plug on it I’ve kept it running in parallel, just to see what kind of variance there is between them. After 48 hours, I gotta say, I’m not seeing any. A lot of the time the readings are actually identical or within 10 units of each other (I’m wearing them both on my abdomen, one on the left and one on the right). The variance increases as I get further out from 100, either way, as you might expect, but still close enough that I feel surprisingly confident about the Guardian being as good as the system I’ve trusted for 3 years. Big relief, that.

Biggest differences maybe cancel each other out: The Dexcom has been a lot more prone to Bluetooth dropouts, while the Guardian3 was a much more elaborate PIA to get inserted and taped down. Those dropouts would be a lot more problematic for running the 670 in auto mode (which I won’t start until next week), so the Guardian’s reliability is significant. On the other hand, from the beginning of switching from MDI to pump therapy I have always really really really hated all the finagling little doodads and whatnots you have to fiddle with to get everything running (failure points! many!), just something that goes against my grain, and I have a feeling the sensor insertion process is going to drive me nuts, vs the Dexcom’s rather elegant simplicity. Ah well, this is what spouses are for.

Also too, and apropos of nothing: turns out I am the first patient at Brigham & Women’s to go on the 670G, so I definitely have the attention of my in-house and Medtronic trainers, both very keen to have this work out well.

Anyway, I’ll keep the dueling CGM experiment going until at least next week, when I switch on auto for the first time. I’ll try to keep y’all posted on how it goes.


Thanks DrBB – I look forward to hearing how auto mode goes! I’m having a tough time deciding between sticking with t:slim/Dexcom as they continue to integrate and evolve, and switching back to Minimed on the 670G.

I’ve used the t:slim since 2013, the Dexcom since 2011, and previously the Minimed Paradigm from 2001-2013.

I bought a used Minimed pump/supplies last year in an attempt to build the closed loop system with my dad, but being on different coasts we never got it together to make it work.

My pump warranty expires next month, and I can either use my insurance to pay for the t:slim integrated with Dexcom G5, OR to switch to the 670G.

Option 3 would be to upgrade to the new t:slim out of pocket ($700), though its warranty would still expire next month. Then I could use insurance to purchase the 670G and have both systems. Use the 670G, see how it goes, and keep an eye on t:slim as new updates come out (next year suspension for low glucose; maybe in 2019 the hybrid closed loop).

What do you think makes the most sense?? My HgA1Cs are in the low 5s so I’m not looking for major life improvements, I’d just like to be woken less in the middle of the night if my glucose levels are headed up or down.


I’ll take Dexcom every time over something Medtronic sells.
Performance, customer service, and Dexcom is a 100% American company unlike Medtronic who stabbed Americans in the back last year: Medtronic, now based in Ireland, still reaps U.S. benefits

Wow, low 5’s–that’s really excellent. I’m reliably running around 6, 6.1, so I’m doing basically ok too, but I have trouble with exercise lows (believe it or not, the 670 is supposed to be able to thwart those) and I’ve had a couple of severe lows of the “Honey, I can’t see, can you help me?” variety that I’m really not eager to repeat. And I’m reasonably tech savvy as well as reasonably good on pump theory and practice, so a pretty good candidate for the 670.

It’s a hard decision right now with the technology so much in flux and things coming down the pike that look great, other than the fact that they’re mostly all still vaporware. Ideal for me would have been a hybrid pump using Dexcom G5, but right now that’s a DIY proposition only, as you say, and I’ve got a low aptitude for gadget building and have other things I’d rather spend my time on. Bigfoot is interesting, could be a contender, but they’ve yet to produce a product and I got pretty burned by their antecedent, Asante, going belly-up with zero notice. I also seriously considered Tandem because of the remote-update thing. Since they’re Dexcom-integrated, I thought there might be a possibility that when they roll out hybrid capability it would just be a matter of getting a software update, since really that’s all the change would be–it’s not really a hardware thing, just a question of what the pump does with the data it’s already got access to. But that’s way too speculative to base any kind of decision on.

Like I said, having to switch from Dexcom to Medtronic CGM was the biggest obstacle for me, and I’m not thrilled about the hard 7-day limit on sensor life or the baroque process of inserting the darn things, but at least accuracy-wise it seems to be up to the job. What finally decided me was the consideration that, if I found I really wasn’t happy, I could always flip the pump to manual, go back to my Dexcom CGM, and be no worse off than before.


Hi DrBB - I’ve been in 670G Auto Mode since mid-August, and albeit still some things to work out (morning high sugars) it’s been GREAT! My main recommendation to you is to learn from others on FaceBook 670G forums, and have reasonable expectations in the beginning. Auto Mode is really “Assist Mode” as there are still a lot of things and decisions the user needs make to be successful with it…give it time, be patient!

Sensor accuracy with the 670G has been fantastic as compared previous Medtronic CGM Enlite sensors. My trust in the accuracy of the 670G sensors has been increasing exponentially! I never used Dexcom CGM so I have no basis for comparing Medtronic vs. Dexcom.

The BIG improvement for me has been having NO LOWs since I went into Auto Mode! That includes a daily intensive exercise program I do which includes 2 hour bike rides at least 3 times a week (I do 75-100 miles of bike riding every week - fast pace, 14 mph) and 5-6 miles/day fast walking on the other days. The tradeoff (for me) has been having a slightly higher A1C, but not that much. My last A1C in Manual Mode was 5.6. Now my calculated A1C with 670G in Auto Mode is 5.9. No bad highs either, but I am careful about what I eat, especially carbs.

Good luck, keep us posted!


Do you have everything you need to build a DIY AP? I remember being overwhelmed at the thought of it - it all seemed far too techy for me - but a friend pointed me to the proper docs, which have been updated and are even easier to follow since I set up Loop - and I was able to get up and running very quickly.

If you can get that going, that might influence your pump decision - might make t:slim more attractive via insurance bc you wouldn’t feel like you are waiting for a closed loop system.

It’s just a thought, considering you have at least part of what you need to get going with Open APS/Loop. It’s nice to have options!

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Very helpful Steve and glad to hear it’s going well for you. I had a really rough time transitioning to a pump in the first place, partly due to faulty hardware (my initial set of reservoirs were recalled about six weeks in) and partly to my own expectations, so this time I’m schooling myself to anticipate an extended process getting it really dialed in. I also eat pretty low carb (less insulin, less hassle) and get my regular exercise via bike riding, so it’s good to have confirmed that the 670 is working for you in that regard.

Haven’t looked into 670 FB groups yet but I will. Any you’d particularly recommend?

Medtronic 670G Free for All
Medtronic 670g Users (you must be in Auto Mode before you can join this Facebook group)

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Just received an email from Tandem minutes ago informing me that there is a software update waiting for me to install that ties the the t:slim x2 pump to the Dexcom G5. Best of both worlds.


Great, good luck with it Kevin23. I seriously considered the Tandem product/roadmap before I decided to go with the 670G. But I did not like the insulin pump functions on the T-Slim as compared to the Medtronic (seemed very klugey, especially filling the reservoir!). Maybe because I am more familiar with Medtronic pump operations than the Tandem? I’ve been using Medtronic pumps for 32 years!

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BTW the 7 day hard time on sensors is not really a hard 7 days, The process isnt as easy as the Dex, but doable. Simply remove the transmitter, charge it back to full, reinsert it into the old sensor, and restart as new sensor.

And you’ll get the hang of taping it down soon enough. I really like the tape set included with the sensors.

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Funny, I was just reading that on one of the 670 FB groups. Someone said if the battery’s still good it’s enough to just separate the transmitter a few millimeters and restart the session. Big relief to know there’s a “cheat,” as for the Dexcom.

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Thanks DrBB for comparing the CGM accuracy. I’ve been using Dexcom since 2013 but am supposed to be starting the 670G in October. I have faith in the accuracy of the Dexcom and am concerned about the switch. Glad to hear they are comparable.

The DIY AP STILL seems far too techy for me – even the forums! – but my dad has been collecting all of the components and seems to have a general understanding, just not the motivation to keep going. I’m pregnant and due in a month – I was hoping to use open loop to keep BG as low as possible, but instead just set a really tight range with the Dexcom and correct with the pump/humalog pen as often as possible.

I think we have everything except the Dexcom receiver and extra transmitters to play with – I dropped the receiver in water and only use my iPhone now. If I end up with the t:slim again, then I’ll definitely keep going with the Open APS/Loop and hopefully finish it this time!

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Also —

After an hour on hold with Medtronic today, they told me the 670G CGM functions won’t be available for people to use until December/January – I guess the pumps are available now, but the transmitters/sensors not for another few months.

The t:slim is a pain to refill, and I hate all of the pieces of trash – that was a difficult adjustment from the Paradigm! Also, I get occlusion alarms about 1-2 times a month, and it feels like when I’m down to my last 30 units, they are completely ineffective, especially for bolusing. That said, their customer service (and Dexcom’s customer service) impresses me, and they seem cutting edge, though less so now that Medtronic won the closed loop race.

About how long does it take to refill the 670G?

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I’m finding that the Dexcom tends to increasingly overstate lows the lower they go, while Guardian tends to understate a bit (or is just being slower to catch up). Just back from a bike ride with both devices giving low alerts: Dexcom, 54; Guardian, 72; fingerstick: 62.

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My son uses the Loop version and does not use the receiver, just his phone for Dexcom data. Just FYI. :slight_smile:

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Not sure if everyone on 670G is using Gardian sensor or some on enlites. I thought there is a shortage of guardian. So still waiting to hear specific news on whether the guardian can go more than 7 days or not.

I can clear that up. The description I got on how to finagle a new session on the same sensor pertained to Guardians, not Enlights. It sounds pretty easy to do. Re Enlites, you absolutely can not run auto mode with anything but Guardians: the system depends on a chip in the transmitter that Enlights don’t have. It may be that you can use Enlights in manual mode; I don’t really know but I think it’s kind of a moot question. They don’t do the training until you have the sensors, and they’re pretty adamant about not trying to use the pump without training (I know because I asked). As it turns out there are a lot of operational differences vs the 630 even though they look the same, so I was glad I waited.

ETA: there is currently a significant wait for sensors. I did the Priority Access program and put in my order in a timely fashion so I only waited a week or two after the 670 came.

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Never actually timed it but I’d guess about 5 minutes for a refill and set change. Hardware-wise it’s the same as a 630 or Minimed. A few more button clicks than the Minimed.