What Concerns me About T:slim X2's Control-IQ

…excited that it’s been submitted to FDA but here’s what concerns me…

  1. My daughter’s infusion sites fail with some frequency in the night, meaning she’ll go high and start developing ketones…how will Control-IQ deal with that? The answer is not to just keep correcting!
  2. Because of #1, her endo has told her to use a pen for boluses to reduce insulin going through her infusion site - does the X:2 have a means of inputting insulin given not using the pump?
  3. My daughter is currently using the Dexcom G4 and it’s reliability is pretty spotty. Is the G6 really that much better?
  4. Related to #3 - the G4’s accuracy drops when she doesn’t keep herself sufficiently hydrated, or sometimes stops reading altogether if she sleeps on it weird - hard to imagine these won’t still be issues with the G6. (A Dexcom rep also told me that the G6 was giving skinny people problems…)
    Bottom line - how reliable will the data be that Control-IQ bases its decisions on?

Interested in folks’ thoughts.



  1. She’s most likely laying on the site and kinking the cannula. Control-iq is not going to help with this.

  2. No

  3. Yes

  4. You still need to stay hydrated for the system to work at it’s maximum performance. Everybody’s body is different. I personally have no issues with the reliability of the G6, except for a bad sensor, I fully trust Tandem’s Basal-iq to rely on the G6.

  1. You can detach the infusion set, give the bolus that you are giving by pen into the air, shake off the insulin and reattach the infusion set. You will be wasting a small amount of insulin, but the Tandem will know how much insulin you have on board.

  2. I’ve had some problems with bad infusion sites. I recently switched to metal infusion sets (Tandem calls them TruSteel) and it helps. I don’t know whether you’ve tried them. I resisted for a long time because it struck me as kind of barbaric to have a metal needle sitting inside my flesh for days. My experience, however, is that they are easier to put in and don’t hurt at all while there so it might be worth a try. You are supposed to change them a little more often (every two days instead of every three).

  3. You can decide how much time your Tandem will tolerate signal loss before an alarm goes off. While it’s not getting a signal, I’m pretty sure it will just deliver whatever your default basal rate is. You could double check that with Tandem.

I am not questioning your observation of the G4’s unreliability with your daughter. I just want you to know that at least some others experience the G4 differently. I’ve been using the G4 for several years now. In fact, when I upgraded to the G5 I decided that I like the G4 better and reverted back to the G4.

I find the G4 to be accurate and precise. It’s not perfect but certainly good enough to provide the glucose data to drive my automated insulin dosing system, Loop.

I can’t speak to G6 reliability as I don’t use that sensor yet. I’ve often if found my sensor is not giving good readings that drinking more water will help.

I do get inaccurate compression lows and I try to affix sensors away from my side as I am a side sleeper.

i certainly think that personal experimentation could help you find how to make the Dexcom sensor work for you. Automated insulin dosing systems, like the Tandem Control IQ, are worth the trouble of trying toget the sensor to work for you and your daughter. Perhaps meeting with a diabetes educator or a Dexcom trainer might help.

This is not even close to being accurate. If the pump doesn’t deliver the bolus, it’s not going to know how much insulin was given by any other means

I’m not sure you understand what @Tnyc’s trying to say. The pump doesn’t know whether the insulin was delivered into the air or the person’s body. @Tync’s tactic of using an “air shot” does incorporate that dose into the pump’s algorithm.

When you deliver by the pen, the pump, of course doesn’t know about it.

Then, when you deliver a pump “air shot,” this folds that dose into the algorithm and compensates for the pen dose.


Thanks for all your thoughts. Will be looking into TruSteel.

The pump cannot keep track of IOB that it did not administer. That was the original question

This is a great solution to site problems. @Dave44 can explain in more detail, he uses them.

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Glad to see someone has seen the light! I keep telling people about Sure-T’s/TruSteel but my positive comments about them tend to fall on mostly deaf ears, which is a shame for those folks who won’t even TRY them!

I hope tandem, like Medtronic is willing to send u samples. There is nothing better than trying for yourself. I despise all cannula sets as they kink so often for me (like as many as 2x a week), irritate my skin with redness, swelling, soreness. Also, the steel sets such as TruSteel are very low profile and u can further protect them from accidental removal by covering them with an IV3000. My sets stay on in temps over 100 degrees when sweating profusely for many hours. They also stay on when spending much of a day in a pool. You can’t cover most of the cannula-type sets due to the way they hook up to the tubing.

Correct. And Tync and Terry have suggested a workaround of getting the pump to administer the same amount on insulin -into the air- as you are administering with the pen, so it’s record of IOB stays on track.


A simple solution to having IOB data accurate when using other means of injecting a bolus.

I too had switched to the TruSteel sets for the same reason as you and used them for a good while now, but I have found that I can’t wear them in some areas as they are too uncomfortable. Even some areas that have decent padding have strange sensitive layers that the steel needle will poke at as it moves around. Combined with the fact that I have pretty much ran out of good real estate everywhere I could use them comfortably, so the absorption has become very poor, I have had to switch back to the soft cannula sets so I could put them in more unexplored territory where I wasn’t able to use the steel ones.

I rarely can go longer than 2 days with either of them, so that is not a factor for me.

As to the original post,

I have a lot of those same questions with regard to the Control IQ. I have significant doubt that it will help me at all as insulin simply doesn’t work fast or reliably for me. Every day is a different adventure, and sites fail all the time, which is the cause of most of my highs. In general, I really don’t think any “artificial pancreas” will work truly well until insulin can work nearly immediately.

I do think the G5 and G6 have better accuracy, though i can’t speak from experience on the G6 as I still don’t have one. It is stopping reading almost certainly because the signal is being blocked, and the biggest issue that really really irritates me with the G5, ESPECIALLY when connected to the pump (which is needed for the Control IQ…) is that is has drastically worse signal than the G4 due to using Bluetooth instead of regular radio signal. With the G4 I RARELY lost signal, even while in another room, but on the G5, I will lose signal sometimes with it literally a foot away. I have had it loose signal for hours, on the pump, receiver, and even phone, with it literally an inch away from the sensor when I had a couple extra layers on while outside in the colder weather. It will sync a portion of the missed data when it gets signal again, but depending on how long it was missing it you may not get all of it. Those missed signal batches can start to mess up the calibration after a while, so that could be a portion of your accuracy issue.

In the end, you will have to upgrade to the G6 if you want to continue using the Dexcom, since the G4 is discontinued and they will not be making more supplies for it.

Is there an announcement from dexcom on this?
That would mean G5 is also done, since they use same sensor.

Unless they’re only discontinuing the G4 transmitter.

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I’d rather they kill the g5 receiver and transmitter.

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Have you had signal loss issues on more than one G5 transmitter?
We haven’t seen anything like your issues, in fact my son usually continues to get readings on his phone even if his phone is more than 6m away through a solid brick wall with thick plaster on both sides - right up to the day the transmitter shuts off. We’ve even had reception on it through 2 walls and the floor sometimes. He has never had any signal loss issues on his pump, even though he usually wears it in a spibelt with the screen facing in to his body.

The BLE signal between the G6 and the X2 is much better then it was between the G5 and the X2.

That is factual. Improvements were made.