Omnipod, Extended Bolus, and IOB Calculation are Incorrect

Hi. Can someone on Omnipod verify something for me?

If my IOB is currently 0, and I give myself an extended bolus of 4 units, 0 now and the rest over 2 hours, the IOB immediately shows 4 units on board. This is not right in my mind.

I have contacted my Insulet Rep about this and she said she will get back to me. But I’m curious if anyone on here has noticed this too?

I rely on IOB a lot so this is worrisome.


I also found the Omnipod’s way of displaying insulin from an extended bolus in IOB as confusing and annoying. I contacted Insulet support about this and they said they’ll "“make a note of it” - whatever that means… I’m not quite sure that I like the way the Animas Vibe does it either, however. I give a 4u bolus, for example and immediately after delivery, the Vibe might display “3.68U” as IOB - what happened to the other 0.32u? (Note - not a specific precise example.) Knowing things, what happens with an extended bolus becomes more confusing.

Using your example, I scheduled a 4U extended bolus with 2U delivered two and 2 over two hours. The Vibe displayed 1.23U IOB immediately after delivering the 2u, and “BOLUS ACTIVE” to indicate the extended bolus – only via multiple clicks thru the Status menus can the amount of the actual delivery and the balance be discovered. This is a very confusing approach, I think.

I suppose I was spoiled by the Asante Snap, which still did not have it quite right, but did better (It’s been a little while, but I think it did something similar to what Omnipod does, but clearly displayed the actual amount of an extended bolus that was/will be delivered. IOB was immediately corrected if an extended bolus was interrupted - that I remember.)

Thanks @Thas. They are scheduled to call me today to “explain” the IOB. Can’t wait to hear this fuzzy math… :wink:

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I have also found the “IOB” to be not accurate. I typically find the biggest inconsistencies when stacking boluses. They ought to use a smarter method–insulin does not work linearly. Glad I’m not the only one to question this.

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Here is the explanation from Insulet engineering. However, I do not agree with it. The IOB on the main screen should always show the actual insulin in my body. They argue that additional boluses need the total “pending” IOB.

For an extended bolus, we treat the part of an extended bolus that has not been delivered as IOB, as if it was delivered now. We do this so that if you go to deliver an immediate bolus while the extended bolus is active, we will account for the amount still to be delivered.
As an example - let’s start with Judith’s bolus of 2.65U, 0.15U of which is delivered immediately and the remaining 2.50U extended for one hour. If Judith takes a BG reading 30 minutes into the bolus, we want to take into account the fact that there is insulin still to be delivered as part of the extended bolus. If Judith’s BG is above her target, we don’t want to suggest a larger correction bolus than necessary given the we still have 1.25U of extended to deliver. The assumption is that she is above target because of the food she has consumed, and that she’s already given herself a bolus dose to cover that food, not all of which has been delivered yet.

That makes some sense, but only so much as the bolus calculator. The IOB should still display the actual IOB. Should that scenario occur, the bolus screen should display suggested bolus - IOB - scheduled bolus +/- correction bolus – that way, should the user desire to take the ENTIRE correction now (and subsequently cancel the extended bolus), they should have the opportunity to do so. Ideally, all those adjustments should be able to be accomplished on once screen - but, I know, I’m asking too much when I use the word “ideal” :unamused:

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No, its not too much to ask for. And I have already asked for it. I’m coming from the t:slim, and they did it right. The IOB on the t:slim would change minute to minute for an extended bolus. As more insulin was delivered the IOB would account for this, in real-time. The t:slim also shows how many minutes are remaining for your IOB. It’s simple math, and it just comes down to how motivated (or educated) the engineers are at Insulet.

In order to form a more perfect pumping experience with accurate IOB info, pump manufacturers could engineer in the actual DIA for the major fast-acting insulins like Humalog, Apidra and Novolog.

Here’s what Humalog looks like. Sorry, wrong graphic! Will update later if I can find the correct one.

On first look, I like the idea. But isn’t this graph an aggregate compilation of the data from many users? I wonder if the n=10 note on the chart means 10 users or one user over 10 meals.

I’d like the ability for me to program in a customized factor that better suits me. I might prefer, for instance, to use 95% of the Humalog insulin action profile or conversely 105%. Given that, I think your idea would be an improvement for almost everybody.

I think most people shorten the actual insulin duration but then compensate for it with other factors, like a skewed basal profile.

Ah, yes. Another reason I love my T:Slim. I like how they put the timeout he home screen, too. For example it will say 1 u from 8pm to 10pm. Makes things simpler.

A little off topic, but this link describes why a shorter DIA is often not a good idea.

Duration Insulin Action

I have mine set at 4 hours.

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I became suspicious that my DIA was set too short when I started to experience repeated hypos in the 4-5 hour post-bolus period. After treating the low, I would check the IOB and it would report 0.0. WTF???

This happened when no other explanation made sense. My basal rate was working well and I had no post meal corrections working. It could only be the last bolus I took. Once I set my DIA to 4.5 and finally to 5 hours and adjusted my insulin to carb ratio appropriately, I no longer experienced this phenomena.

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Sorry, my bad. I used the wrong graphic image for the DIA. Still, the point remains that the data is available and could be programmed to allow a selection, or allow a user-defined DIA like we have today.

Actually, thinking about it a bit more, it’s surprising that the FDA allows a user to define a 3 or 4 or X-hour DIA. That creates a fundamental risk of inaccurate IOB calculations and creating unforeseen consequences.

Interesting discussion. I’ve had several replacement Vibes now which ALL calculate IOB incorrectly in my opinion. Animas never get back to me about it, just replace the Vibes, which all do the same thing. My issue is with any bolus - extended or not - whatever DIA I set in, the IOB shows a (diminishing) figure up to 2-3 hours beyond this DIA. For this reason I currently have a DIA set in of 4 hours (Humalog) as I know it will give me IOB for up to 6 > 7 hours’ later, depending on size of bolus I.e. if too small, not noticeable. I have to confess I have quite an erratic lifestyle and eating habits, and am very maths oriented, so I tend to roughly calculate my own IOB anyway & never rely on my Vibe.

I wrote about this a few times on different pump boards & found some other Vibers who’d noticed the same issue with their Vibes. I suspect not all Vibes do this, but from what I was able to gather, a significant no. do. Bad algorithm which Animas seemed loathe to address!

It’s always good to know there are pumps which get these things right, showing it can be done!

Okay, here is a bit different graphic, taken from the Lily Humalog page.

Again, what I would like to see is a menu option for my pump settings that lets me select “Humalog”, or “Novolog” and then the DIA gets populated into the bolus calculator based on my insulin type, not an arbitrary time.

FWIW, I don’t believe there is a pump that does anything close to this, including the t:slim. My impression from the t:simulator that I used was they use a straight line calculation like my Accu-Chek, with the difference is that the IOB is always visible.