T slim question

Hi all. Here’s what happened:
The other morning i ate a small breakfast bolused 1.13 units, felt the vibration indicating the bolus had been delivered.

About 15-20 minutes later I decided to eat a larger meal, looked at my pump to bolus and there wasn’t any IOB.

I’ve had this happen to me before I just didn’t think into it that much but now it concerns me a little.

T slim said that I couldve had negative insulin amounts of board. This doesn’t make any sense to me. I also did not have any IOB prior to the 1.13 units. They are adamant that the pump is fine and that the reduction and no bolus is normal. Insight, anyone?

To provide a better answer to your question it would help to first have some additional context on how you are using your t:slim pump.

Does your t:slim support C-IQ? If so, do you have C-IQ turned on? Whether or not C-IQ is enabled determines how the pump will calculate your Insulin On Board (IOB) value.

Yep. I assume that you are using Control-IQ because it’s the only reason you’d see quirky IOB things like this. With Control-IQ, the IOB is a net value, modified by whatever insulin the pump added or withheld, in addition to the usual time-based degradation.

Since Control-IQ can adjust your insulin in both directions, IOB is less to do with boluses anymore, and more about potential to lower BG. It only shows insulin that is above your baseline basal amount. If you were below 112 and the pump reduced your basal, then the amount of reduced basal would be subtracted from your IOB.

It may seem confusing, but it makes sense.

If you’re not sure the bolus was actually delivered, you can click on the upper right hand corner of the screen to see the status page. Your last bolus is listed there.


@Robyn_H is certainly correct that IOB calculations with C-IQ can be a big funny. However. I would look very carddully at your pump logs for a period of 2-3 hours before the bolus in question for maybe 2-3 hours afterwards. I would suggest looking at the Complete log under Options → History → Pump History → Complete.

On multiple occasions, I have failed to hit the final Deliver on a bolus and, a bit later get an Incomplete Bolus Alarm. If your alarm settings are on vibrate, that alarm notification can seem a lot like the Bolus Completed vibrate …

I hope that you learn something of interest by examining your pump logs in detail.

Stay safe!