Dexcom G6 and Tandem pump

I’m going to be starting a Tandem pump next week after MDI. I use the Dexcom G6 and wondered what happens when the G6 is wildly off readings and how the pump handles that? If your meter is vastly different is there a way to manually make a pump adjustment?

@DFBB , you should not be having those problems. I have been using Dexcom products for more than 20 years. Since the release of the G6, my cache of test strips have expired several times over. I work with multiple specialty doctors and all five have agreed that finger sticks are no longer needed. The greatest difference between a lab glucose and my CGM has been 14mg/dl.

The one thing my team and i have learned is you should position yourself and your glucose to a level position prior to and for the 2 hours after sensor or sensor transmitter swap outs.

CGM changeout

There is a mountain of communication protocols with checks & balances buried in CGM communication.

I have been using DexCom models for 20+ years.

Everything starts on the pump because it is the ‘medical device’ and the primary display device even if a phone is used personally as the primary device. This is further emphasized because a pump and dedicated Dexcom receiver cannot be used simultaneously as the Dexcom receiver is classed as a medical device.

Pick your best time. Your best time should be when the CGM report shows level data and you are not planning a meal or generally needing to bolus during the following two hour window. This means select a time when you have a 3 hour window of usually level CGM reporting.

For me, 7:00PM is the best time to have level CGM reports and the time is free of BG changing activities for me.

If I am doing a sensor only, I change sensors at 7PM. At 6:55, I get everything read, do a skin prep and insert the new sensor by 6:58.

At 6:59, I go to my phone and stop the sensor, then to the pump and begin the stop and start at 7:00.

When you are ready to insert the sensor, (1) make certain the skin pre liquids are DRY, (2) the inserter is FIRM against the skin, (3) then , break off the orange safety, and (4) pressing firmly, fire the inserter. The firm pressure should insert the sensor & minimize misfires. Follow the remaining pump on screen instructions.

As soon as the pump is done, I go to the phone and repeat the process. I enter the code on each.

I sit back and watch, assuring both the pump and the phone are playing nice together.

If it is a transmitter, again it is the pump that is the key player.

I start at 6:55 by stopping the transmitter session on the phone then the pump and start the new transmitter and sensor on the pump from transmitter to sensor.

Once things are going on the pump, on to the phone and repeat the process.

About 7:10 with either a new sensor or new transmitter and sensor, I verify both the pump and phone are playing nice.

Here are links to the information supporting this supportive recommendation:

Hope this helps.

I’ve been using the T:slim X2 and a Dexcom G6 for a couple of years now.

It does happen. It’s rare. But sometimes the Dexcom can take a day to get on track. I’ve had a few times where on the first day after I inserted a new sensor, it was certain that I was dangerously low. Just set up one alarm after another.

Dexcom support said not to worry about it and sometimes it just takes 12 hours or so for a sensor to fully “wet” and adjust itself. (I know with my old Medtronic Guardian sensor, I’d have times where I would hit a capillary or something on insertion and that would completely throw off the sensor.) I told them I’d calibrated several times, and they said not to calibrate more than a couple of times a day. Apparently it can confuse the algorithm or something. They said to just leave it alone overnight and calibrate in the morning.

So, to your question, Diane:

  1. If it feels off, calibrate.

  2. If that doesn’t work, leave it alone for a while.

  3. If the pump is consistently well off the mark, you can turn off Control IQ. The pump will then ignore the sensor and just give you a steady basal rate. (Whatever default amount you and your doctor decided to program in. For me, it’s 2 units/hour.)

  4. When doing a bolus, you can always override any of the numbers. You can manually enter a BG value (whether or not there’s a sensor BG from the Dexcom). You can input whatever carb number you think is right. And you can just manually tell it how many units to give you.

  5. Once the sensor is back on track, just turn Control IQ back on, and everything will go back to normal.

  6. If the sensor continues to be wildly off, you may have to pull it out and replace it. Call Dexcom support first. They’ll mail you a replacement sensor so you don’t run short.

It’s all totally manageable and you can use common sense. Hope this helps :slight_smile:

Hi @DFBB . I see you’re used to Dexcom and will be adding a pump. You probably already know not to expect the readings to be identical, as CGMs read from interstitial fluid while fingersticks read from blood. I have had a few that were exact but a CGM is considered accurate if it is within 20% of a meter read. That may not sound reassuring but unless you’re low that 20% difference - which is the max - probably will not make a huge difference in the big picture - a CGM read of 100 could be anywhere from 80-120, and you can always treat if you feel 80 is too low. The pump with CIQ (or BIQ) adjusts based on Dexcom’s readings, but if your fingerstick is wildly different you can calibrate the CGM on the pump: the Dexcom number will adjust to one midway between its prior reading and the number you entered from your fingerstick.
I’ve learned to trust my Dexcom readings so I only do fingersticks one in a blue moon unless my body feels different from what the sensor is telling me; as @987jaj says they’re typically very close - mine may be off by more than his 14 points but the readings fall within the 20% margin of error.
You can certainly do a manual bolus if your fingerstick reads higher than your Dexcom but be cautious. It may be due to lag time between the fingerstick reading and the CGM and it’s generally not recommended to add additional insulin unless you realize you forgot to account for some carbs. I used to rush to bolus when I saw the dreaded :arrow_up: arrow(s) but I’ve learned to wait a while to see if the numbers level off, which they typically do.

Diane @DFBB you ask some very important questions, and you’ve received good response. BUT, I very strongly suggest that before using your new pump that you read, and understand, both the Tandem User Manual and the Dexcom User Guide - your questions are answered in those documents.

My question to you is why do you believe your G6 readings are “wildly off”? What are you using for comparison - a most probably less accurate BG Meter? Keep in mind, that the US FDA has approved the Dexcom G6 for use in calculating a bolus, it has never approved any meter for use in this manner. As you have learned, the Tandem t-Slim x2, when CIG is installed, has a sensor calibration function; it is advised by both Tandem and Dexcom that this feature should only be used [read the Tandem and Dexcom website FAQ] when differences, with multiple readings, exceed 20% difference.

best wishes in your new system; I’ve found the CIQ has been a wonderful assist for me since the first month of its release.

Thank you all so very much for the info. I found it very helpful. I’m hoping that when I meet with my Tandem trainer this Friday many of my new pump user anxieties will go away.

Great articles and info, thank you for taking the time to answer so thoroughly, very helpful.

Thanks so much, the tips and tricks that other T1’s have to share are awesome.

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Thank you! I so appreciate this forum.

It can happen that the Dexcom is wildly off. We have had issues with that with my daughter - in fact I think we had a whole lot of sensors that had that issue as it was almost a regular occurrence for a while that they either failed on warm up or were wildly off. once we ordered a new lot, they were much better. We always test a few times in the first few hours after warmup. If they are off just a little, we don’t do anything, since they often do settle down after 12-24 hours. If they are wildly off to the extent they would impact dosing significantly, we calibrate. We have never had to turn control IQ off, but that is an option. All in all, it’s a good system and definitely makes things easier.

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When i have to calibrate a sensor I usually do this right after getting up. I normally find that my BGs are the most stable (not rising or falling) when I first get up (not been exercising, not been eating, and no stress (yet :-), etc. You can really do it when you BGs are horizontal for at least 20 (but ideally longer if possible) but I find when I first get up is the most accurate

Never calibrate after exercising or eating since these tasks will most likely not provide the ‘stable’ BGs you are looking for to do a calibration.

My experience has been significantly different from most pump users and G6 users. I’m still trying to find reliable sites for the G6 and infusion , so I’ve had a chance to see so-called “bad sensors” . My experience is that there are no bad sensors. There are bad sites and improperly installed or contaminated transmitters*. (* Two clicks are good, one is not. Dry shiny contacts are good, ones with moisture between sensor and transmitter are not. )

I’ve kept very detailed records of my experiences, and had to be convinced that the equipment was reliable, and in the process learned how installations can fail and how to test and troubleshoot bad sites. I’ve never subscribed to “when in doubt change it out”. Automobile mechanics refer to this as “using a parts cannon.” Truly changing it out would mean replacing everything.

I had sites that were bad from the start, others that became erratic 2-3 days after a mediocre start.
By bad I mean the sensor reading didn’t change value by more than 10% while my BG went from a before meal low to a peak By mediocre,I mean that the outputs went up and down in the right directions, but never reached within 20 mg/dL of either the stable highs or lows. ( Calibration doesn’t change sensor range, it adjusts the offset so it’s close at one value.) Mediocre sites became erratic after a day or two, readings jumping up and down similar randomly while my BG was stable.

I’ve used both versions of Tandem software recently . it doesn’t matter which one you’re using neither one of them works in auto mode during the two hour warmup. Imo no pump should be used in an IQ mode until AFTER you’ve verified that a new sensor is working reliably.

It depends how well you want to manage your BG, how much to trust the “no calibration” sensors. They can take up to 6 hours to stabilize within spec in a good site. Having experienced +30% site failures during my first two weeks. I don’t trust a new sensor site until l’ve tested it against a BGM at least twice.

If you read the manual and trust that the people who designed the pump know what they are doing you will have a BGM and unexpired strips, if for no other reason than for emergencies. Equipment is just as likely to fail during a 4 day holiday as the four day work week that follows.

And how can you tell if the CGM sensor is working well if you haven’t a BGM for comparison?

Anyway, I change sensors in a way where I know with the least effort in the least time whether I can trust the site. I only change sites between meals when my BG is changing slowly and I’m not going to eat for more than 2 hours. . I check my BG before I change a sensor. After it warms up, I record the BGM and CGM values. I immediately take enough glucose tabs to raise my BG by 30 mg/dL. I check my BG and the CGM reading before my next meal and when I estimate that my BG will be approaching peak. If the CGM is within 20 mg/dL of the BGM within the next 15 minutes, it’s trustworthy.

Of my last ten good sites, 2 were that close within 6 hours of insertion. Nine were good by the next meal. One required calibration.

After I think it’s good, I check the CGM against the BGM the next time I’m stable low and decide whether it’s close enough for me or needs calibration. That’s 5 -7 BGM tests pers sensor.

I also test infusion sites, with a BGM test after a change, a glucose tab challenge, and a pump-calculated correction. By mealtime I expect my BG/CGM to be within 20 mg/dL of prechange level and falling. The BG/CGM level 3 hours after a balanced meal should be within 60 mg/dL of preprandial and falling.

I suppose to folks struggling to get their TIR under 75% what I’ve done sounds like a lot of work. It really wasn’t.

My “advantage” (though my wife would say it’s a handicap) is that I’m a general engineer. That used to be a thing. Figuring out how to do things with little help is half of what I was trained to do.
Once I decided what I needed to do, and how to define success, all I had to do was determine how I could measure it. What to do then was obvious, and the problem became a procedure.
The other half of what I do is document my work so anyone can duplicate what I did. It’s not the only way someone could have done it. It’s one way that I could that works. It was easier than solving the emotional control problems I had during my first decade with T1D.

Very impressive work. Thank you for sharing.

I don’t believe that what I’ve done so far to preserve my safety and my health is impressive. It was just common sense systematized by an engineer. I won’t guess when I can easily get empirical data.

Those tests were the minimum I could do and have confidence that the equipment is installed in reliable sites. Once I get my reliable infusion zones mapped out, I should be able to simplify and the number of BGM tests/sensor site will drop closer to 5.

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Thank you for your very thorough info.

use a test strip to check your sugar and if wildly off do a calibration, you can put the calibrated reading on your tandem x2. Sometimes you need to check to see if your g6 is being correct. It happens to me, check ,calibrate and move on. It happens. Good luck

Like dbmmccarthy68, our daughter’s Dexcom G6 BGs and her finger stick BGs have sometimes been wildly disparate. Control IQ can only base its “decisions” on what the G6 relays to it. We calibrate at times but have learned that we should not do it often. As a result, we have to ignore the beeps at times. That’s especially annoying during the night but it can’t be helped. My daughter has learned not to trust the low alarm at night so she’ll do a finger stick. Inevitably her finger stick BG reads higher than the Dexcom says; also often off by more than 20%. But better to play it safe.
Nevertheless, I can’t adequately express how much I appreciate (and rely on) these devices! Game changers for us!

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