OmniPod: The IOB Issue

As a follow-up to my latest OmniPod report, I have done some homework on the Insulin on Board (IOB) issue. Of course, I couldn’t let this go :)

It turns out I opened a big can of worms, ’cause this feature is highly complex.

First I queried Insulet Corp. on why they made their IOB (aka BOB for “bolus on board”) function work the way it does: it currently shows only insulin delivered as a correction — and not remaining insulin from a meal bolus — therefore it can prompt the user to take a post-meal correction too soon after eating if the BG reading is too high. When I posted this, some folks shouted that this approach was “disconcerting” and potentially “a big safety issue.”

Hmm, representatives of Insulet tell me that during product development, they surveyed a number of doctors, and the consensus was split fifty-fifty on how to handle IOB. Some pumps, like the Paradigm, apparently treat IOB exactly the same way. But many others do consider remaining meal bolus, and based on this, block the user from taking another meal bolus while a previous one remains in the system. In other words, if you wanted to eat an additional apple after a meal, the pump wouldn’t let you bolus for that food while it still sees an active bolus dose.

Insulet apparently wanted to give users the freedom to bolus again without hesitation. But of course we have to be careful. This can lead to insulin stacking and lows.


However, the Insulet folks did say that considering customer feedback on their IOB function is “on the top of our priority list for future development.” I guess I’m not the only one tripped up by it.

Meanwhile, I also queried a couple of pumping experts on the whole IOB/BOB function, and their thoughts on safety and efficacy:

* Virginia Valentine wrote back to me, saying simply, “I would agree that using only the correction for the IOB does not make sense.”

* John Walsh, author of Pumping Insulin, had A LOT more to say –

“I have had a few Paradigm patients and talked with several others who are in relatively good control except that they have “unexplained” hypoglycemia that is sometimes frequent. Unexplained, that is, until I show them that their pump is not subtracting any BOB when it is in excess of their correction need from the carbs they are eating. The recommended boluses in these two pumps as well as in the Animas (when the BG is above target) will be excessive whenever the BOB is greater than the correction need.

From my unpublished data, this situation arises in 1 out of every 9 boluses (or about every two and a half days for the average pump user), although I would estimate that in only 1 out of every 20 boluses would the dose be sufficient to cause a significant low. Well over two-thirds of boluses are given with BOB present.

This danger is offset to some extent by the relatively high average glucose levels for most pumpers, but I cannot explain the logic for why these pumps were set up to handle BOB in this way. The engineers appeared to lack direction from a competent medical board. The only rationale that I have been offered after much questioning is that “All carbs need to be covered by a bolus.” Well, excess BOB is exactly that, bolus insulin. Why any excess bolus insulin taken earlier in the day should not count as much as a current bolus baffles me.

Two other things need to be kept foremost in mind for an accurate BOB calculation. The first is whether the duration of insulin action has been correctly set. Many pumpers set their DIA too short. When they do this they hide the true activity of their boluses.

The second is that BOB is only calculated after a BG has been entered
into the pump. The pump cannot accurately account for BOB unless it has
a BG to make a calculation for both carb and correction requirements.

Unfortunately, only about 1 out of 7 boluses has both a carb intake and glucose value entered at the same time. Most pumpers are doing blind bolusing.”

Eeew, that sounds scary. Since I’ve actually had relatively few lows since starting on the OmniPod in February, I guess I’m flying pretty well “blind” over here.

In any case, if you want to learn more about how the D-industry handles BOB, see John’s latest presentation on the issue, especially slide 19. This man knows his stuff.


22 Responses

  1. EmilyS
    EmilyS May 31, 2007 at 8:10 am | | Reply

    There has been a big discussion about this recently on the list at, with many supporters for both systems. One point that I think is important to note, just as insulin isn’t instantaneous and may still have some BG lowering ability hours later, neither are the carbs you eat instantly available. Depending on the fat and protein content of your meal, your food could still have some blood glucose raising power a few hours afterwards. The pump doesn’t take this into account; it cannot know if your blood sugar would still go up without intervention. As much as I appreciate my pump taking some of thinking off my hands, I am not ready to hand it over entirely. There are just too many variables.

  2. Kelsey
    Kelsey May 31, 2007 at 8:47 am | | Reply

    I echo Emily’s comment… I have a Cozmo pump and it calculates IOB by taking meal boluses into consideration. When I first started pumping, I’d enter my blood sugar 1-2 hours after a meal, say at bedtime, and the pump wouldn’t offer a meal bolus for a small snack. I experienced a fair number of high readings after trusting that feature. Like Emily stated, the pump can’t know what we ate, whether it had a lot of fat or protein, and thus how much our blood sugar will rise from a previous meal.

    Somethings we’ll just have to think about ourselves. I for one feel much safer that way.

  3. David Edelman
    David Edelman May 31, 2007 at 8:49 am | | Reply

    Thanks for sharing this and doing the extra research, Amy. At the very least, it probably helps to know exactly how your pump handles this scenario. Then you can at least be aware of what is causing some of the those unexplained lows and take preventative action.

  4. carol
    carol May 31, 2007 at 8:59 am | | Reply

    Very informative post. Thanks Amy! I have a Cozmo, which includes all boluses in the IOB calculation. Pretty much at any point, I can override what the pump is recommending, and do so frequently. Can you override with the Omnipod? Thanks for posting John Walsh’s presentation. Interesting on the insulin duration usually being set too short. Guilty as charged — I’ve set mine at 3 hours. May need to rethink.

  5. Scott
    Scott May 31, 2007 at 9:01 am | | Reply

    I am inclined to side with John Walsh on this one, although the earlier versions of pumps that had IOB/BOB had many, many, many complaints that the companies made the duration of insulin completely arbitrary. The explanation was that it came from the clinical trial results from the insulin manufacturers, except that this tended to overlook the fact that analogs work differently in everyone. I think the newer pumps resolved that issue by enabling people to customize their duration of insulin activity, but it does strike me as a tad stupid to tell someone they cannot bolus for more food if there is already insulin on board, as if we might not consider eating again (I’m thinking about Thanksgiving or other holidays, for example)?

    The real issue is that no insulin works the same in every person, and similarly, the efforts to close the loop seem to overlook this annoying little fact, so I don’t think the artificial pancreas is quite ready for launch anytime in the immediate future!

  6. shannon
    shannon May 31, 2007 at 9:32 am | | Reply

    My son uses the cozmo and we rely greatly on the IOB. The thing to remember is that the pump will allow you to do a full bolus for all food, just do not enter the blood sugar each time.Which makes since,I would not enter a bg if he ate only and hour or so prior. I only enter the bg if my son is way under targer or higher than 300.

  7. Tim
    Tim May 31, 2007 at 10:08 am | | Reply

    I’m woefully out of touch with the pump technology. I’m still using a Minimed 507C after almost 10 years. It’s the most amazing piece of technology — it’s lived in my pocket all this time with not a single malfunction. It doesn’t even know what a glucometer is, let alone want to talk to it.

    Reading about the extra tubes or bulges, or calibration, or headaches from pumps attempting to think for me makes me hope that it lasts even longer for me.

  8. Ed
    Ed May 31, 2007 at 10:41 am | | Reply

    What a timely post, I’m in the process of deciding which pump to go with. I spoke with a minimed rep right before reading Amy’s blog today and we actually discussed the difference between IOB corrections. I guess the minimed wizard automatically adjusts the next correction for the full amount of carbs coming in. Does anyone know/ understand how the Animas 2020 reacts to this?

  9. kendra
    kendra May 31, 2007 at 11:01 am | | Reply

    Thanks so much for this post, Amy. I know my DIA is probably too short – 2 hrs – but I’ve had less highs this way. I rarely have a “wtf, where did THAT come from?” low…but I also rarely rely on my bolus wizard calcuations. (MM 715 pumper here.) When I’m “insulin stacking” I’ll treat things as if I have a 1:10 ratio and bolus for food that way, and I rarely run into issues with lows. I’ve never been a heavy bolus wizard user, because I think it falls under GIGO..garbage in, garbage out. If you’re not 100% sure your settings like correction factor, active insulin time, and insulin to carb ratios are exactly right and you don’t understand exactly what the pump is doing when it calculates, you shouldn’t use it.

  10. Suzanne
    Suzanne May 31, 2007 at 12:05 pm | | Reply

    I don’t know about the Animas 2020, but I use the Animas IR1250, and I can ALWAYS override whatever it suggests. You still have to be smarter than the machine and always bolus for the carbs you’re consuming. I find the Insulin on Board feature helpful when I’m tempted to RAGE bolus to drive down a pesky high blood sugar.

  11. Brent
    Brent May 31, 2007 at 12:28 pm | | Reply

    My 15 yo daughter uses the Minimed 515 pump and, contrary to what John seems to be saying, it definitely takes existing bolus insulin into account, whether carb or correction. At least when using the Bolus Wizard.

    For example, if she eats a meal and is within her glucose range when she boluses for that meal (i.e., no correction) and then tests a couple of hours later, it will not let her correct for the full amount that she might manually calculate if still on injections, taking into account the curve of the insulin action we have set (4 hours).

    It will also not let her stack correction boluses, always subtracting existing correction on board within the insulin duration curve in the calculation.

    The key to the confusion may be what John says, in that many people do not enter their current BG and/or carb reading when bolusing, and do not use the Bolus Wizard.

    Since we started on the diabetes bandwagon only about six weeks before she got her pump, we’ve awlays relied on the Bolus Wizard, which absolutely, definitely, takes both carb and correction boluses into account in its calculations.

  12. Challenge Diabetes
    Challenge Diabetes May 31, 2007 at 1:55 pm | | Reply

    IOB (aka BOB) Ruling

    Thanks for the investigative research Amy.  You certainly went to the right sources in Virginia Valentine and John Walsh (aka – Mr. Insulin Pump).
    While there are always design considerations that go into technology (pros vs cons), some features need …

  13. michelle
    michelle May 31, 2007 at 3:32 pm | | Reply

    We do the same as Shannon with the cozmo. If my son is eating soon after a meal bolus I simply do not tell the pump what his blood sugar is and I allow the pump to give the full bolus for food.

    The issue is – with most pumps (I can’t speak for OmiPod) but you can override what it says. You still need to be smarter than the pump.

  14. AmyT
    AmyT May 31, 2007 at 5:36 pm | | Reply

    Of course you can also override with the OmniPod, Folks! Sorry I neglected to make that clear.

  15. Jonah
    Jonah May 31, 2007 at 6:48 pm | | Reply

    If I were to pump, my biggest reason would be wanting to do multiple boluses during a meal; bolus for firsts, bolus for seconds, bolus for deserts.
    It’s a part of why I’m getting Iports.
    I wouldn’t get a pump that wouldn’t allow multiple boluses in whatever time frame I wanted.

  16. Lauren
    Lauren May 31, 2007 at 7:40 pm | | Reply

    Since I’m so recently diagnosed, I am injecting insulin — when I first heard about the pump, it sounded like a nightmare. I couldn’t deal with the idea of “wearing” my disease. Now that I’ve struggled with lows and highs and all the baggage that comes with daily injections, I’ve begun to consider the pump. Anyway, I had someone show me their pump’s “bolus wizard” feature, and it gave me a headache. So many variables! I don’t mean to turn this thread into a “to pump or not pump” discussion, but I’m definitely interested in others’ experiences. Does the bolus wizard really simplify your life?

    I hope to enter medical school in fall 2008 (are you listening, admissions committees?!) so my goal is to be on “auto pilot,” comfortable either injecting or pumping, by then!

  17. Felix Kasza
    Felix Kasza May 31, 2007 at 11:36 pm | | Reply

    Either John Walsh is wrong, or I am too stupid to understand what he is saying.

    If there is excessive IOB (i.e., greater than the correction needed for the current BG), my Paradigm recommends no bolus.

    If I _additionally_ eat carbs and tell the pump about that, it will suggest the full carb bolus. Why? Because the BOB covers previously eaten food, of course, or a previously needed correction. Hence, the current food intake is included in the suggested bolus. D’oh!

    What it boils down to is this: The only ways to get excessive BOB are:

    - incorrect basals
    - incorrect I:C
    - incorrect correction factors
    - incorrect carb estimates
    - incorrect digestion estimates (bolus speed vs. digestion speed).

    Nothing Walsh can say or do will alter that, and nothing he can say or do will prevent me from going low if my I:C is way off, or if I take the full bolus for a pizza all upfront.


  18. Felix Kasza
    Felix Kasza May 31, 2007 at 11:40 pm | | Reply

    Hi Lauren!

    The bolus calculations are actually easy. Once you figure out how much insulin you need, roughly, for a given amount of carbohydrates, you can do it in your head.

    But the automated bolus calculations in pumps do make life simpler: They remember that you may need, for the same meal, more insulin in the evening than in the morning; if you wish to correct a high BG two hours after a meal, the pump will tell you that you still have enough active insulin to bring that high down; and so on.

    Not to mention the pleasure of being able to turn down a basal rate temporarily and go to exercise an hour later, as opposed to being on Lantus or Levemir and going to the gym with a steamer trunk full of glucose tablets and energy bars!


  19. travis
    travis June 1, 2007 at 12:51 am | | Reply

    I’m fairly recently DXed as well (6 months), and waited far too long getting a pump. Not only will it prolong any honeymoon period you may have, but I think it’s a pretty safe bet that you’re going to get one eventually. Barring new islet cells, pumps and CGMS seem to be the definitive direction in type 1 care. So the sooner you start, the sooner you’ll just get used to it.

    As for my pump, I’ve got the (relatively) new Animas IR 2020, which has lots of bolus options. IOB includes corrections and meal boluses. If you use the ezBG function to try and correct a high, it will subtract your IOB, often making the reccomended does 0. With the ezCarb function, however, IOB is not considered, so that extra apple could be bolused for with a problem. Also, if you enter a high BG along with the carb number, it will factor in a correction as well, and if you enter a low BG along with the carbs, it will beep at you and tell you you’re stupid.

    It’s a pretty good system I think.

  20. michelle
    michelle June 1, 2007 at 7:20 am | | Reply

    Jonah, that’s exactly why the pump is good. That’s totally what we do with my son – especially when we’re out to eat. I can bolus him first for what I know he’ll eat, and then continue to bolus during the meal for extra food he’s eating. This way I get the benefit of an upfront bolus, but he can eat what he feels like without me stressing. MOST pumps will do this…since most parents do bolus this way for their children, I think we’re getting some conflicting info. We all do it this way, regardless of what kind of pump we have.

  21. Penny
    Penny June 1, 2007 at 1:29 pm | | Reply

    My son has an Animas and I’ve found that I just have to decide whether to subtract the insulin on board myself or not.

    The Animas will show you how much insulin is on board even if it doesn’t subtract it.

    I’ve found that if Riley eats a longer-lasting carb meal, such as pasta and I subtract the insulin on board when I give his next bolus than he may end up high. Because, the insulin he had on board was still covering the carbs he had floating around.

  22. Lauren
    Lauren June 1, 2007 at 9:36 pm | | Reply

    Thanks for responding to my pumping questions! I am definitely a novice. I agree that I may just be delaying the inevitable by not initiating pump therapy … I have an “overcorrection” problem and tend to drive myself low, so the IOB feature could really help.

    Thanks guys!

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