TSlimx2 IOB on display page

Question (this may have already been discussed) - I have a tslim pump and have recently noticed the IOB will sometimes show a different amount immediately after I give myself a bolus. For example, a few days ago I was 234 and gave myself a 4 unit bolus, up from the recommended 2.79u. Almost immediately after (less than 2 minutes), the IOB said 1.08. To me, this didn’t make sense. I understand that with time, the IOB will decrease according to the algorithm. However, to go from a 4 unit bolus to showing I only had 1.08 on board was surprising. Then, to make things a bit more weird (for a lack of a better word), about 50 minutes later and after no more boluses or basal corrections, my IOB went up to 1.89.

I called tandem 3 times asking why this was the case, and specifically if my pump was malfunctioning. The tech support rep told me that she wasn’t 100% certain that it wasn’t malfunctioning. She even asked to call me back approximately a week later so she could ask her colleagues about what was going on, and still couldn’t come to a definitive answer that my pump was acting normal (or wasn’t malfunctioning).

Has anyone else had this experience or noticed it? Obviously the big concern is, if I give myself 4 units, but my IOB (displayed in the middle of the pump screen) immediately after the bolus says 1.08, I’m inclined to think the pump didn’t give me the full 4 units thus I should give myself more insulin to get to that 4 unit amount. If this didn’t happen to me before or if I wasn’t aware of this, I could have given myself the additional 3isn units to make up for that amount. In total, this would mean I gave myself approx 7 units when my pump initially recommended 2.79. I find it odd that Tandem would have the IOB centrally located on the insulin display screen while it could be this misleading.

Maybe I’m missing something but would like to know if anyone else has had, or noticed, this phenomenon.


Welcome, @ [Kevinzero11

My Tandem has never done that to me. I would follow up and demand that they check the pump out. IOB is one of the most important things a pump tells you, and if it is not working it’s a serious problem. It is supposed to work.


This happens to me when there has been previous 0 basal suspensions (red line on T:Connect app graph).

It seems to consider some bolus as netting out the missed basal. But just my guess. Eventually mine levels out without any action on my part. I primarily watch cgm trend.


Hi, can you explain a little more in what you mean? I want to say that this issue occurs indiscriminately, or in other words, the pump is acting normal without any CGM alerts, low/high blood sugar, and/or expected blood sugar post-bolus.

It’s almost unimaginable that the tandem reps don’t have conclusive answers on this given how misleading it can be.


Your situation may be different than my experience, since bg was >180. When CIQ predicted bg over 180, pump would give auto bolus. That may have adjusted the correction bolus you did, due to bolus initiated by CIQ.

Did you review pump history?

I use sleep mode 24 hours/day, so don’t usually trigger a CIQ bolus.

I should have been more precise and said that the screen updates after the bolus is delivered. When you program the bolus, the screen goes back to the home screen, showing the pre-bolus IOB. When the bolus has completed a couple of minutes later (the screen will be dark by then) you wake it up by pressing the main button and then the bolus should show in the IOB.

Yes… I have noticed the same thing with mine. I’ve given myself a Bolus and noticed it wasn’t what I had asked for. Didn’t think much of it until I read your post. I am definitely going to keep an eye out on it and call them and see what they say. Sorry for your experience and having to deal with Diabetes

Reading this thread just after for the first time noticing a much smaller example of this with my pump, and wondering about it. I had set a 10 g carb, which would ordinarily give a 1.0 but pump told me would be 0.96 because BG slightly under goal. However, when I looked at IOB just after bolus, it said 0.81 rather than 0.96. But, “last bolus” says 0.96, as does pump history.

I have certainly looked before many times, and never noticed this discrepancy.