Measuring IOB

Hi, I’m a new T1D parent, but I work in tech and am starting to explore the DIY tech side of the T1D world. My daughter is on the Dexcom G6 and omnipod and I’m struggling to wrap my head around the IOB “safety” feature. Our CDE advised that we set IOB to 3 hours, but I’m finding that to be a completely arbitrary number, depending on the time of day, activity, etc. In the mornings, it’s too long; in the evenings it’s too short; and during her recent growth spurt, I believe the IOB feature existed solely to drive me crazy.

I’ve read through some threads here, but still have a few questions:

  1. Is there any tech out there that measures concentration of insulin in the blood stream?

  2. How do you manage the IOB feature from day to day? Do you consider this feature differently when you have a particularly active day?

  3. Being new, I still fear the double arrow down. So when my daughter’s numbers run very high, I’ll partially correct with a bolus and then bump up the basal as well. Do bolus and basal impact IOB in different ways?

Any thoughts would be appreciated, or feel free to redirect me to other threads if these topics are covered elsewhere. Thank you!


For us, this is mostly an indicator for us of how much we may need to correct in the event a meal doesn’t react as anticipated and starts pushing him down into low territory. We calculate how many carbs need to be consumed to account for the IOB so that he doesn’t end up low. Besides that, it’s just to see how much he has in his system so that you don’t end up administering too much…it keeps track of it so that we don’t have too.

For us, insulin is insulin. It’s all Novolog…whether it’s basal or bolus, so we don’t see them as much different because they’re really not. It’s called something different and they serve different purposes, but the impact is pretty much the same…too much and BG’s will fall. Too little and they’ll rise.

We used to fear double down and double up as well, but we’ve learned how to correct SOONER for lows and MORE AGGRESSIVELY for highs. We used to correct his “double downs” at 130 but that was never early enough and Liam always fell low. The sweet spot for us we’ve found is treating at between 150 and 170 depending on how fast he’s falling (how many numbers). And for highs, as soon as he has double up and is over 150, I do an immediate 1/2 unit. I wait and if it goes over 200, I give another 1/2 unit. On top of this, if it’s a high starch food, I’ve got a temp basal going of 95% more basal insulin going into his system for 4 - 6 hours.

We are sugar surfers here so we react to the moments (more in line with the way the body and pancreas work in non-T1’s). The key we’ve found is to not “over react” one way or another. Trust the science. If you know you gave 15 carbs and that should be enough, wait it out. Too many times we’ve ended up giving 30 carbs or more and he ended up skyrocketing 30 minutes later to over 400. We give and just keep testing and if he doesn’t go much lower, we just wait it out.

As sugar surfers, though, part of reacting to the moments are also in knowing when to suspend extended boluses and temp basals as well as know that you overshot it and a carb correction may be required. It’s just watching the “trends” and reacting to them…not so much worrying about the individual tick marks and the BG’s at present.

Remember, the intent of the basal is to keep the BG level in FASTING periods. And bolus is intended to treat the mealtime insulin requirements. Whatever combination you find works for you to control your lows and highs I don’t think anyone will ever say you have done incorrectly. Diabetes if very much YDMV, especially how and when insulin is administered as well as what types work best and where. If you find a system that works, just pat yourself on the back and hope it doesn’t change for a long time! But, if your child is anything like Liam, what works today can be drastically wrong tomorrow. :stuck_out_tongue: We just roll with the punches! We use a combination of everything the POD has to offer to control Liam’s sugars. Bolus, Basal, Extended Bolus, Temp Basal, Suspend options, different basal profiles for different times (sick -vs- not sick for instance), etc., etc., We do it all.

Sorry for the rambling. :slight_smile:


If your daughter can skip a meal, you can always measure the insulin duration, by giving some insulin, skipping the meal and seeing how long the insulin continues to bring your daughter down. This is really difficult at night because growth hormones get dumped once or twice if your child is growing. Then you can set your pump more accurately.

At this point, we don’t fear double downs unless they are at 90 or less, then we treat aggresively, but a 180 double arrow down will turn for us with the automatic reduction in basal his pump applies, and sometime a couple (like 4) carbs to get a roll out at 80-90.


On medtronic pump, iob is only bolus amount, and how fast IOB drops is determined by active insulin time.

So if you are doing basal, it would not be included.

But you could do a dual bolus that is both part immediate and part extended over the time you set. So then the extended part would be included in iob.


Not sure of terminology for omnipod, but if setting to 3 hours, it probably refers to Active Insulin Time, not iob.

This means if you do normal (immediate) bolus of 2 units, then after 3 hours, it is used up (no longer reducing bg).
After 1.5 hours from time of bolus, the IOB shown on pump would be 1 unit, since half the time has passed.

But maybe omnipod uses the term differently ??


OmniPod uses “Insulin action”

System setup > Bolus/basal/calcs > Ratios/factors/targets > Insulin action > Highlight and set the amount of time you want.

  1. Other than having something in a vein, no. However, they have done studies where they do measure insulin concentration in the bloodstream over time and then they extrapolate that to the entire population. For a while I was kind of obsessed with this question since I didn’t really care what the IOB was, I cared about how much insulin was in my son’s bloodstream lowering blood sugar right now. I think at one point I convinced myself that it was the time derivative of the IOB, but I can’t remember my thinking on that. In the end, to make that insulin activity or concentration number relevant required a level of statistical analysis and number crunching I never got around to. But I agree it’s really what we all care about.

  2. IOB really matters for considerations like when to treat a low and with how many carbs. I definitely evaluate it differently for different activities. That said, three years in we’re not really at the stage where we can perfectly predict that, say, he’s going to be running around a ton and so that’s why he’ll be running low with very little IOB, or that he’s sitting around on spring break like a lump and therefore will be running high even with 1 unit on board all the time. Instead, I notice the trend over the day and then adjust my expectations in the moment – so more like sugar surfing. But the time it takes for me to adjust my sense of what’s normal is quicker now. So instead of waiting two days with stubborn highs and persistent IOB, I might switch to a higher basal and more aggressive corrections after, say, 12 hours.

  3. So, basal and bolus, especially on a pump, are delivering the same type of insulin. The same amount of insulin from one should be the same amount as another. That said, when you are delivering basal insulin, it’s constant. (Also, note that a 0.4 unit/hr basal rate translates to more than 0.4 units of insulin in the bloodstream at peak concentration) Anyways, when you are bumping basal up you are ensuring a constant, higher level of insulin is reaching her blood stream. I don’t know for sure, it’s just my pet hypothesis, but I suspect that with insulin resistance, you need a certain insulin concentration in your bloodstream for a certain amount of time, in order to give receptors in the liver the time to switch into “take up glucose” mode rather than “spew out glucose mode.” A basal is going to more reliably provide that higher, steady level. You can do the same thing with constant corrections. But if you think about it, a large correction may provide a transient spike in insulin concentrations in the bloodstream, but you’d be surprised at how quickly those dissipate to pretty low levels.

As for the 3-hour IOB – I think you mean duration of insulin action (DIA)? In any case, most studies suggest it’s actually closer to 5 or 6 hours physiologically – but that doesn’t mean that’s what’s going to work best in your pump. If you’re finding that, say, she’s going low with negative IOB or something at one time of day and going high with persistent positive IOB, to me that’s a sign not that the DIA is changing in her body, but that she has different basal needs at different times. The best way to test that is by doing a fasting test (which sucks, i know)…if her blood sugar stays steady (within 30 points) of its starting point with no food or insulin added, then her basal is all set. If not, you need to tweak basal. It’s also possible her carbF or ISF are off, and if, for instance, they’re off in opposite directions and the true DIA is longer than you’ve got programmed, you could get some unexpected effects.


Also an important consideration for DIA is the type of insulin being used. Different insulins have different curves.


So, just thinking out loud…
For a rough sense of how much insulin is active at any given time in the bloodstream, I think you could ballpark it retroactively from the difference in two blood sugar measurements five minutes apart. So if your blood sugar is 150 at time=0 and 100 5 minutes later it dropped 50 points in 5 minutes. And I think insulin in the bloodstream is “used up” in about that same amount of time.

If your ISF is 100 (meaning 1 unit of insulin drops you 100 points), then that means 0.5 units of insulin was active in your bloodstream over that 5-minute period.

But actually I don’t think that’s a great way to get at the true value as ISF changes dynamically; you’re more insulin resistant at higher blood sugars and more sensitive below the hypoglycemia threshold. On the other hand, the plus of this method is that it’s accounting for a drop from both basal and bolus; it’s just saying that in order to get such a drop, you probably had X amount of both basal & bolus insulin active around that time. I think using the time derivative of the IOB you are not accounting for the possibility that your basal rate might be incorrect.

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Thanks, all. And yes, I was using IOB and DIA interchangeably - primarily because there is no “true” data behind the IOB number, just the DIA setting. Apologies for the confusion in terms.

I think this number crunching, curve drawing activity is where I’m headed next, short of any actual reading from new tech. It would be great if some of the new AP technologies built in insulin concentration measurement.:pray:

I’m still choosing my battles, and skipping meals isn’t one I’m ready to fight yet. But I did test at 3am this morning with no IOB and knowing that growth hormones are probably mixed in there, but wanting to test both the correction factor and DIA. It looks like the insulin stopped working after 3hr 15 min and the correction factor is holding steady around 1:200. Pretty sure these numbers are inaccurate in the afternoon, but again, one battle at a time. (I’ll have to search the forum for a thread on “battle fatigue” next… :sleeping:)

This still begs the question re: the concentration of insulin in the blood. At 3am, she had none, but if this were mid-day and we were at the tail end of an earlier dose, those numbers would likely look different. Which brings me back to hoping for a sensor to measure IOB concentration.

This summarizes my question perfectly. We’re coming off a growth spurt when insulin had zero impact through breakfast and lunch, and then suddenly her numbers crashed at 4pm each day. My sense was that the insulin concentration had built up all day and then suddenly something changed and it all kicked in at once. Maybe it’s the “liver modes” you mentioned and I’ll have to read up on that aspect.

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This is the type of behavior we see when our basal is too low. We were having all kinds of problems recently, that were corrected once we got our basal dose titrated better.

I’m still choosing my battles, and skipping meals isn’t one I’m ready to fight yet. But I did test at 3am this morning with no IOB and knowing that growth hormones are probably mixed in there, but wanting to test both the correction factor and DIA. It looks like the insulin stopped working after 3hr 15 min and the correction factor is holding steady around 1:200.

As long as you’re sure your basal levels are right at this time, then that works. But it’s tricky because your basal can be almost right, or right for part of the night, and then change at others. We have been doing some basal testing in bits and pieces (i…e, if our son sleeps late we basal test an hour of the morning, if he spurns dinner, we basal test at night, etc.) We’re finding that bits of ours are right and then his basal does seem to change more than we initially thought. Because he’s small, a difference of 0.025 can change whether he’s holding steady, dropping or rising.

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I was having that issue myself for longer than I care to admit (years) and in my case, it was the cumulative effect of meal boluses that were stacking up and finishing their work when I thought they were tapped out.

For example: I was given advice to eat more at breakfast to gain weight. So I did. Breakfast is a challenging meal to “get right” in the morning, as we all well know, due to wake up hormones, etc. I thought my bolus wasn’t doing hardly anything as I’d go into lunch at a 200 if I was lucky. Then I’d bolus aggressively for lunch, but the insulin hadn’t had a chance to beat down my bg yet and I was adding food on top of it (even with a 30 minute pre-bolus). Then I’d correct in the afternoon and bolus for a snack, and it would finally start to get down to my ideal bg range. Then I’d drive home from work and my crash would be starting right about then…and I’d need half of my usual insulin dose for dinner because of all of the stacked boluses in my system.

So now I am much more conservative in my breakfast composition. I make sure I am in range before I eat lunch. And I keep tabs on meal and snack boluses closer than four hours together, bc adding them up and adding them closer than that can really make my bg spin off in some fun directions much quicker than I’d expect.

So I’d guess that your daughter’s meal boluses might be doing the same thing, and I’d guess that your insulin duration is truly longer than three hours, but I could be totally wrong.

If your daughter enjoys deli meats, cheeses and the like, you can fool her by giving her as much of that as she wants as her “meal” so that you can still do your testing. Just a thought.


Nice idea @ClaudnDaye, I hadn’t thought of that. I can certainly ask my son to skip a meal without issue, but I really like the sneaky way. I may try that.

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It’s so tricky to trouble shoot too because a too high basal rate can be “off” for an hour or more and only then start to impact numbers. In general, I think the thing with insulin is that at any given time, you just need X amount of insulin, so 3 wrongs can make an almost right a lot of the time. Meaning ALL the settings can be wrong and yet add up to roughly the right amount of insulin you need most of the time – except for a few stubborn periods when people run low or high.

Except the basal, of course.

That’s a lab test, not something you can buy like a glucometer or ketone stick for ad hoc measurements at home. Sorry, but you should forget about measuring that.

It’s unlikely that the cause is insulin somehow hiding out in the body unused and then suddenly becoming active. The observation you report suggests the insulin dosing needs tuning.

The observation “insulin had zero impact” just indicates there was insufficient insulin. This could be from insufficient basal, or from too weak an insulin:carb ratio. The standard advice is to tune the basal first, to provide a stable foundation that makes it easier to understand cause and effect when analyzing BG excursions. Unfortunately, tuning the basal is kind of like tuning a guitar: you can get it perfect, but it won’t stay that way.

The observation “suddenly her numbers crashed at 4pm each day” makes me think there’s too much basal. If it were too much meal bolus at lunch, there could be a drifting down at 4pm from the tail of the insulin action (for Novolog and Humalog the actual duration of insulin action is around 5 1/2 hours—even though pumpers tend to use shorter numbers, when using algorithmic closed-loop control it can become important to use the true value.) But you describe it as a crashing at 4pm, which sounds like too much basal for the circumstances. (Is someone running around a sports field at 3pm? Exercise increases sensitivity, so basal generally needs to decrease for exercise.)

If I were quietly at home and my BG crashed at 4pm each day, I would decrease the basal a small amount starting at 2pm or 2:30 and would expect that to reduce the speed of the crash the next day. I’d continue decreasing a small amount each day or second day until the decline no longer happens. For me, adjusting the basal by “a small amount” means 0.025 units per hour. Like decreasing from 0.25u/h to 0.225u/h.

Back to the question you originally asked (amended to call it DIA.) The duration of insulin action should be handled as a constant. Don’t think of it as varying depending on time of day or activity. For general pumping, 4 hours is a reasonable number. It’s really not a useful knob to turn anyway. (Except for people trying to run the 670G pump in closed loop. They adjust DIA as a desperate work-around for the limitations of that system.)

The first parameter to adjust is the basal schedule. The goal here is to adjust it so the BG doesn’t tend to rise all by itself or fall all by itself in the absence of other influences. A good basal schedule tends to be stable for a few months, maybe changing with the seasons. A principal exception is in women who are cycling monthly, look up T1Allison’s thread on that. The basal schedule is a bit elusive because “absence of other influences” almost never happens. So the goal here is to set a basal schedule that doesn’t show a regular pattern of drifting low or drifting high at the same time each day, even if a meal is skipped.

Once the basal schedule is set, then we routinely use temp basals to handle the changes in insulin sensitivity that our bodies experience during exercise, illness, hormone spikes and so on. Some people set temp basals several times per day, to prepare for exercise or to help handle unexplained BG excursions that we blame on “hormones”.

The insulin:carb ratio is fairly stable in my experience; it drifts quite slowly for me. Dialing it in can be a challenge even after the basal schedule is good, because meal-related BG excursions have to do with two factors, namely the amount of insulin and the timing relationship between the speed of insulin action and the speed of digestion (which changes greatly depending on the composition of the food.) Speaking in broad-brush, if the mealtime BG curve shows too high a spike initially, but then the BG goes low around 2 or 3 hours later, you wanted a smaller dose of insulin but given earlier before the meal (“pre-bolusing”). The digestion released carbs into the bloodstream before enough insulin was there to handle it, causing a rise, but then there was too much insulin that hadn’t been used up by the amount of carbs eaten. A different pattern is the BG that rises but then plateaus rather than coming back down. This suggests that more insulin was needed. Could be from too weak an insulin:carb ratio, or could be from a meal heavy in protein and fat, which releases additional glucose into the bloodstream over a period of hours. (We generally handle that by a “dual-wave” bolus that gives enough up front to handle the carb spike, and continues to deliver additional insulin for a couple or few hours to handle the extended digestion.) So anyway, the goal of adjusting the insulin:carb ratio is to remove a regular pattern of “I always end up high after eating” or “I always go low after eating”.

The third knob (after basal schedule and bolus strength and timing) is the correction ratio AKA insulin sensitivity. In practice we select a number that generally seems to make corrections work ok, and then we don’t change that number. Do corrections always seem to cause a crash? Weaken the correction ratio. Do corrections always seem to leave our BG too high? Strengthen the correction ratio. But we’re going for “generally right” on this parameter, because in practice, corrections rarely work right because of so many confounding factors. My practice is that I watch the CGM and make additional adjustments with insulin or carb to steer the BG in a good direction based on clues I see in the graph. (This practice is called “sugar surfing” after the title of the book by Stephen Ponder.)

I’ll stop now. It looked like OP was seeking novice’s guidance, but I have a tendency to induce TL;DR.


That is certainly possible and none of us can know for sure.

And managing relatively new T1D in a child is obviously a dynamic situation for a variety of reasons. I’m an adult managing it in myself and I get enough challenges with just myself working on it.


is what makes me think looking at prebolus timing and DIA would be (1) the easiest to test for and (2) the most likely culprits. Especially given that basal testing is helpful but not terribly possible right now.

ETA: The whole time I had the afternoon crash problem, my basal was right on the money. Every time I did a fasting check of my basal, it was dead on. And maybe that has no application to this problem, but the high points of the problem line up so it is something I would consider.

Stacking meal boluses can lead to insulin gaining steam in a sneaky fashion. Obviously basal issues can trip things up, too, but practically speaking, the most helpful thing as easily and quickly as possible to check would be looking at the spacing of the meal doses and just being mindful of that.

That’s all I’m saying.

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Also don’t forget that Honeymoon is a real thing. It causes crashes in Liam still with zero IOB and Basal turned off all night long sometimes. So many variables…


Good point :+1:

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