IOB disappeared with T-slim

Has anyone using T-slim X2 had this issue?:
Using control IQ, I gave bolus of 1.35 and 15 minutes later it said IOB 0??? How does that happen?

I notice this when I see that basal was reduced, increased or suspended based on cgm. My understanding is that it counts some of the +/- basal amount to adjust IOB.

Here is some discussion on it.

Yes, IOB is now a net value of any insulin delivered that is above and beyond your set basal rate. (One of the many reasons basal testing is important, because it affects whether the right IOB is calculated.)

There’s no way to actually remove insulin from your body, but what Control-IQ effectively does is redirect surplus insulin to be used as basal insulin instead. Hence, the reduced IOB.

It cannot display negative IOB, if there is ever more insulin withheld than your programmed basal rate.

It takes a little getting used to, because it’s very different than what you may have been used to before, but it really is a good change. It’s the only feasible way to account for insulin adjustments in these “living”, constantly changing AID systems.


Thank you for the explanation!

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It’s the OpenAPS approach; a negative IOB means that we have less IOB than our basal implies is required. In other words the IOB displayed is the actual IOB minus the prior requirements of the basal.

My understanding is that Insulet uses a different approach and displays the true IOB; it accumulates all insulin deliveries. This is historical; Insulet always did this, everyone else always ignored the basal. Alas only one approach makes sense.

That is awful. I don’t use control iq or any of the methods that deliver insulin controlled by dexcom and never will. I would not want my iob calculated by anything except what the bolus was and when it was given and what the duration is. This is super important for me. I would never include basal changes in iob. Basal on a pump is given slowly and imo should not be lumped in with larger boluses or corrections as iob.

It actually does make sense. Before, one took a different insulin for basal and once the dose was given it was there and could not be altered. So IOB was exclusively calculated on what one could control… the bolus and the correction insulin. Since the new pumps use exclusively one kind of insulin, its measure can (and should) be allocated as IOB no matter whether it is basal, bolus or correction. I believe that is the John Walsh concept that the Tandem algorithm is based upon (remember John Walsh of “Pumping Insulin,” my insulin bible of old?)

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Funny how everyone’s perspective is different. I see control IQ as a safeguard for if I screw up. In fact, with the initial post I submitted where my bolus had disappeared, if I hadn’t gotten that whole bolus I would have needed to treat my guaranteed hypo. Thank you T-Slim!

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That is not what it seemed you said, it seemed you said you bolused and it was recorded, so you did get the bolus, but then the pump erased the record of it for some reason after 15 minutes.

You seem to have missed my point, my point is I would not want my pump erasing boluses that I did due to basal etc. because boluses are given in large doses and the duration is different than basal which is given in small doses, slowly, per hour.

In any case I would not use any of those things on the pump because I don’t want dexcom controlling my insulin since it’s not always accurate enough to be safe for me.