Huge disparities between CGM and BG readings (670g)

Back again with a question regarding Medtronic 670g and Guardian 3 CGM. My hubby will be switching to t-Slim/Dexcom early next year, but in the meantime we are noticing a common trend. His CGM will read let’s say, 120. But the pump is asking for a BG. So he tests and his actual BG is 170. Pick a number, any number, and the disparity is often 50 or more. It also works in reverse. The CGM will say 190, but a BG will say 112. The pump won’t even have down arrows indicating he’s dropping fast in some of those instances. We will assume that the BG is the most accurate(?). Of course, like many, he is experiencing the CONSTANT requests for calibrations, finger sticks, etc. Hence the reason he will be switching, and the fact that Medicare doesn’t cover the Medtronic CGMs. Anyway, in order to be able to switch to the t-Slim, we were told by the rep that there needs to be something “wrong” with the 670g, or insurance will not cover it. Warranty is up (4 year) on Feb 5. Would these disparities indicate an issue with the 670g’s continuous loop system? Is this a CGM issue? It seems like the pump works, but why are the readings so messed up? His endo strongly recommends the switch also, because of the far superior technology. We are trying to get our ducks in a row, but also in the interim, it would be nice to know what is going on between the 670g and the CGM. Any thoughts, comments, suggestions? Many thanks.

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Yes the guardian/670 system is terrible. My daughter is still on the pump but uses dexcom instead, so no closed loop. I dunno if that’s good enough for the insurance company. Since they let her switch, i guess so? We didn’t request to switch pumps too. Should have.


I’ve got the same issue with the 770. You could make adjustments to the various settings as that might reduce the number of alerts you get. My new endo thinks Medtronic is subpar compared to Tslim.

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Yes, he has changed many settings to no avail. I think Medtronic has really lots its luster with its diabetes division. Glad we didn’t upgrade to the 770 since you aren’t the first to say it has the same issues. If we get pushback from our insurance company for coverage, we would consider paying cash for the t-Slim just to get out of this conundrum. We do know that Medicare will cover the Dexcom CGMs.

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I’m sorry to hear about your issues - thankfully his warranty is up soon but it’s still frustrating. In the meantime he could go manual, turning off his CGM and loop, and using fingersticks instead - assuming he feels they are more accurate; and correcting on his own. It’s what we did when the early pumps came out.

I don’t see why you wouldn’t be allowed to switch once your warranty is up - that’s the ideal time, and it’s what I did, although it’s been a while. Maybe things have changed, but it’s also possible your rep meant you couldn’t switch “without cause” until the warranty expires.

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I have almost exactly your situation and once I get Medicare will be making that switch:
1 no more weekly 12 hour sensor warm up periods
2. Closer BG readings
3. Smaller pump -30% I hear
4. Readings thru iPhone app
5. Over the air upgrades/updates
6. Dexcom CGM coverage and accuracy

Medtronic has most certainly lost its market and clinical leadership in this area although I will say their support is superb. Usually.

In sum, I concur all the way with your observations. Great luck!

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Yes, he has done that before, but he is a guy who goes low at night more often than not. We need the alarms! I’m thinking that the Tandem rep meant we could only get insurance to cover a new pump IF the old pump was acting up. Until the warranty ends, we are stuck with it. After that, a new Rx can be filed for the t-Slim.

I’ve had similar issues from time to time with great disparity between finger stick and Guardian CGM. But, I think that also happens with Dexcom, based on what I’ve read and my experience when I had Dexcom. I will say that I found a great improvement in the numbers when I switched my sensor site to my upper arm. My torso did not work well for me for Dexcom or Medtronic.

Still, there are so many issues with the Medtronic 670 G……I’m going to figure a way to switch to TSlim. I had been thinking that my warranty was up in Dec 2021……but no. It’s up in Dec. 2022! Regardless, I’m switching ASAP. I have to for my mental health. I can’t take it anymore. The last couple of months it’s started doing Sensor Updating always after 10:00 p.m. Who knows how that will turn out. Sometimes, it resolves itself, other times I’m told to change sensor at 1:00 a.m. It’s sadistic really. It will be a happy day when I can part with this device.

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February won’t come soon enough for you but it’s now a few weeks away. Your doctor might start the process early so everything will be in order as soon as your warranty runs out and you don’t gave an additional lag getting your devices.
I’m assuming you still need to go through training for Basal IQ/Control IQ. When I got it a couple of years ago it was done via online video and you had to pass a couple of quizzes before you were approved to start. You can still use Dexcom as a “plain old CGM” in the meantime but you need a link and authorization to do the training so ask your doctor what they can do on their end to cut down on delays.
From what I found on the forum at the time, many if not most people were fine with the online training. I still had some questions afterwards and I covered then with my rep. Since you use a loop now the online training may be enough - just keep in mind you’ll need to do it unless something has changed.


I have all those issues and finally took myself out of smartmode. I have slept MUCH better in manual mode - still have to calibrate every 12 hours, but no BG requests otherwise. I also have suspend before low on, which is useful. I actually have had less lows with manual mode, because it will suspend, and I can figure out what I have on board much easier, since there wasn’t any Smartmode basal corrections to think about. You do need to be more watchful for higher numbers and correct, since it’s not doing that for you - but, since I’m stuck with this pump for another 14 months - it’s the best I came up with.
If you can switch to Tandem - do it! My son has Tandem and there are WAY less issues!


All good advice. He still has CGMs through mid-March, so he’ll use those up. He sees his endo in the middle of this January, so he’ll ask about getting everything in order when the 670g warranty runs out. Interesting that you can do online video training…his endo told him their diabetes educator would be training him in. But it’s nice to know that there are additional options. She also mentioned that there would be more insulin wasted due to cartridge-filling methods with t-Slim. We did know that already. It looks like once you have a few loads under your belt, it’s not all that intimidating.

The BIQ/CIQ training may have changed since I did it a while back but they’ll set you up with what you need. BTW, TSLIM plugs in to charge rather than using batteries, but it’s a quick process even using a “charging brick” as I typically do. That’s an issue for some, no biggie for others.

Can you expect to fully charge the t-Slim while in the shower? Or are you possibly able to charge it while connected to your body with an external charging device connected? (We often use a small portable USB power device for charging our phones on-the-go while away from the house.) How long does it take to fully charge the t-Slim if you did it every day while showering? We did know it’s a plug-in, but don’t know the actual charging times.

@Stephanie_Y this is from the Tandem web site

A single battery charge on a t:slim X2 pump can last for up to seven days during normal use without CGM and up to five days with CGM. The best thing you can do for battery health is to charge your pump each day for 10-15 minutes or until it is fully charged.

Just like with a cell phone, the more often a display is turned on, the greater the impact on battery life. Things you can do to help minimize this on your pump include:

  • Clear alerts, alarms and reminders as soon as they appear
  • Set your Screen Timeout setting to 30 seconds (default). Options > My Pump > Pump Settings > Screen Options > Screen Timeout

so it depends on how long you shower… if you shower in <5 minutes you are not going to be able to completely charge it.

it seems (IMO) to be a crazy pain in the neck to charge the pump while using it - the manufacturer does not have a battery pack or boost charger for the pump and disclaims “only Tandem charging accessories can be used”. but apparently the pump uses common USB power configuration so you can charge it from a computer which may be handy in an extended regional power outage. cheers. good luck.

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I plug in while I’m reading, at my desk, in the car (car charger), watching TV… I keep my pump on the sink while I’m showering so I don’t lose connection with the transmitter - that would cause my pump to alert and I’m very sensitive to out of place sounds. Those would drive me crazy until I got out of the shower and went to turn it off, greatly disturbing my relaxation. They would catch up when they were “reunited” so it can be done. I rarely go below 20% - at which point I get battery warnings - but even at 20% I can be back to fill part in easily less than an hour. Probably half that.

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Hi Stephanie,
So sorry your husband is having so much trouble with Medtronic. I started on one of their pumps and switched to Tandem as soon as my warranty was up for many of the same reasons, even though this was on the Medtronic 530 and Enlite CGM. So disappointed to hear that they have not improved.

Anyway, while I am not on Medicare yet, I would suggest discussing with his doctor who takes care of his diabetes (Endo or Promary Care doc) all of the issues he is having. Then ask the doctor to submit a request for the Tandem pump and Dexcom CGM. The reason I say this is that having worked in the pharmaceutical insurance field I can say almost for certain that your husband will need to submit for Prior Authorization to get the new pump. The insurance company will then request documentation from his doctor that supports the request. So, it is very important that his doctor is aware of all of the issues so that he or she can document them.

That’s the best advice that I can offer. I hope he can switch soon!

Pam K
T1D 57 years and counting!

Hi again. Another delayed thought: have you - sorry, has he tried adjusting his overnight basal? It’s not uncommon to have to tweak them now and again. I’ve found just a tenth of a unit down or up can make all the difference for me so it’s best to start small, give it a few days to “settle in” and adjust further as necessary. Come to think of it maybe it’s time to do a basal rate check.

His endo already tried that. It was refused. Since he is only a month away from the end of warranty, we are not pushing it. And yes, the t-Slim will definitely require a prior auth in any case. I’m encouraged by all the responses here. Thanks for your info too.

Yes, already tried that countless times. Sigh. But turning temp basal on for the night is the best course of action for him (fewer alarms). At least we then only get the one beep signifying the end of temp basal period.

Sigh. At least you found a workaround for the time being.

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