Min. BG for bolus calculator

I asked our CDE and our Omnipod rep, too, but I’m interested to hear what you all think:

Last night, our daughter was 83 at bedtime, so she had some cheese crackers. I gave her 18g, which was probably too much, but I figured better high than low. We didn’t use the PDM, because we’ve just never even thought about bolusing when the point was to bring her up before bedtime.

Sure enough, she woke up at 146. Don’t get me wrong, I’m happy that we were generally in the right ballpark — and as it happens, that’s pretty much bang-on what would be expected using her ratio and correction factor for that hour, so let’s hear it for having nailed the PDM settings, at least for the moment! — but then I realized: we have this great technology, and I bet if we’d told it she was 83 and taking 18g, it would have bolused for the appropriate portion of the snack. She’d have woken up closer to target without going low, and I wouldn’t’ve had to worry about the math when my brain was tired. So,

  1. In the future, should we tell her PDM she’s 83 (or whatever) and tell it how many carbs, and let it reverse-correct at bedtime? (I feel like that’s an obvious “yes,” and we should have known it all along, but I’m checking because what if I’m wrong about that); and

  2. Why is there a range for the min BG for bolus calculator (50-70)? I’m guessing that if you’re under-70 low, you should have juice and get back up into a safe range before you then have a snack that you might bolus for. But if that’s the idea, then why allow it to be as low as 50? Are there times where you’d bolus when you were 50, even while taking glucose?

hi @srozelle I bolus when low when I am “eating the fridge”, that is , knowingly killing the correction. insulin is slow and sugar is fast, so if I am 50 , and eating carbs, say 60 grams, I’ll bolus to the “top of my range” (for me 120 mg/dl) so it works like this 50 to 120 is 70 mg/dl I want to rise and for me I need 14 grams carbs. so my bolus is 60 grams, minus 14 grams, I bolus only for 46 grams carbs.
My medtronic “bolus wizard” will use bottom of range when I am below target, for me 90 mg/dl, so if I use the program it will bolus me for 52 grams, which I might not want to do, I don’t know pod programming specifically. If I was going to lie, I would tell my pump I was at the top of my range, not below my range.

The medtronic will also scream not to bolus under 70 but will do it anyway. .or I have a choice to enter no blood sugar and just bolus for 46 grams (my typical strategy). I can also choose to deliver that bolus over 30 minutes if I really want to come up first and then cover the extra carbs. I can also manually bolus and completely override all built in safeties.

for the pod you will need to know if you are lower than target, if it picks your low target (I can only bet it does)

for question 2, there is a range, (most likely) so you don’t bolus under 70 so you don’t get into serious trouble.

I don’t know if this is helpful. sorry if I made it worse.

Definitely helpful, thanks! Omnipod could have a target range like that, but we were told to set it for a specific target (so it’s set to “target 100, correct over 100,” for example).

So you DO bolus when you’re 50, just sensibly bolusing for the correct amount to get you to your target, and you’ve figured out how to use your Medtronic to accomplish that.

As for question 2, it sounds like you’re agreeing I’ve got the rationale right: it’s to stop someone from bolusing when they’re low. And I guess they’ve decided that some people want to be saved from themselves sooner than others. So, like, you’re comfortable bolusing at 50, but for sure when we were first diagnosed, the endo wouldn’t have wanted us trying that.

There are sometimes those stubborn lows that need repeated treatments (before always frustratingly ending up too high), so that’s the risk: that you’d bolus during what turned out to be one of those. Has that ever happened to you, that you know of?

@srozelle That’s a good point. I should clarify. If I’ve been working all day, or active, I can get a low that requires 5x more carbs to correct, and it’s usually because my liver is making and storing glycogen. Yes I wouldn’t typically take insulin. I would correct the 14 or 15 grams and wait. Then repeat if it didn’t work. That’s what I do practically 90% of the time I should have said that I only bolus while low, very occasionally, it would be for if I was low, didn’t eat a proper meal, nothing else going on.

Don’t forget that I learned to be able to tell because I didn’t have a finger stick or CGM at first. There was no way to tell if I was 75 or 150mg/dl because the urine test would come up zero unless you were high. I could only tell I was low by feel, so you get a 6th sense about you, including if a correction like 15 grams was going to work. Been like that always for me.

A friend of a friend used to show off a party trick (back before CGMs), guessing his BG and then doing the finger stick to check. Seems you’re not the only one: his accuracy by feel was legendary. :sunglasses:

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@srozelle , in retrospect you made the right call, and did what I would have done IF I had observed either by finger-stick, CGM, of “feel” that my BGL had been falling and would probably continue to fall. The difference …

Knowing that the PDM, or pump wizard, only gives an estimated bolus, I would have entered the carbs and BG into the device and then adjust any insulin dose. My reasoning being that a device calculator does not know what I’m feeling, or if I might have had some exercise during the day that may be in-play. In a situation like your daughter, I may have infused a small fraction of a unit - but caution should always rule.

As to “target Range” of 50 - 70, this is telling the calculator to only add insulin to the “food bolus” if BG is above 70, and only deduct when below 50. Personally, I would never have a target that low - scary!

Thanks, Dennis! I’m not sure I’m understanding what you’ve written, but that 50-70 isn’t a target BG. It’s the minimum below which the Omnipod won’t let you deliver a bolus, presumably to stop you from inadvertently bolusing when you’re already low.

Although… it got me wondering. I saw on my daughter’s recent lab work that the “normal” A1c is 4.0-5.6%. And then I went looking, and found this chart that says a 4.0% corresponds to an average BG of 50:

Our DNE was considered “aggressive” for teaching us we didn’t need to correct with juice until 65 (though since that was what we were taught, that is what we do, and it seems to work fine).

So I was truly shocked to see an average of 50 is considered “normal.” Especially in light of this other resource that lays out what various stages of low generally mean, and it starts at 70:
https://www.uofmhealth.org/health-library/aa20831

So what gives?

@srozelle , I misunderstood what you were saying about the “50 - 70”. It makes sense to me to block insulin delivery when low, especially around 50.

My LabCorp HbA1c lab report provides a reference of 4.8 to 5.6 as non-diabetic; an A1c of 5.0%, in my charts means an average 90 day BGL of 90 mg/dl. A 4.0% A1c would equal 60 mg/dl. I certainly would not want to have my BG hovering around 50.

With the pandemic keeping me eating home-cooked meals, my A1c has been consistently 5.5 or below - the endocrinologist was very concerned until I told her, and my Clarity and t:Connect reports confirmed that I’ve avoided hypo events. I first told the endo that the lab made an error reporting my A1c at 5.3 because my CGM 90 day average report was 117 mg/dl; then three months later when I had up to a 5.5% my CGM average was 120 mg/dl which should equal 6.0. Go figure.

The recognized “In Range” is, as you say 70 - 180 mg/dl and that a person with diabetes should have TIR of at least 70%. The way I interpret this is, that we should not let our BG go below 70 mg/dl - I have my “warning alert” set at 86. Dexcom Clarity defines “Very Low” as 50 mg/dl or lower in one place and as “54 or lower” in another.

So, what gives? My thought, set our own range and goal at a place where one feel comfortable but a range that presents a challenge. Instead of the 110 mg/dl standard range with a goal of 70% or higher, I set my TIR in a range 75 - 170 for daytime 12 hours and 85 - 145 for night 12 hours with a goal of 90%. I accept the Clarity texts telling me the days I miss my goal - and then try to figure how I could do better.

The conversion charts are all over the place. Here’s a current ADA one that says a 4.0 (which really is the bottom of the reference range as per the point-of-care test she just had done at Johns Hopkins All Children’s) means an average BG of 68 — that’s pretty different from 50:
https://www.diabetes.org/diabetes/a1c-test-meaning/a1c-and-eag

The chart I linked to before is a .net, on closer inspection it’s not something I’d rely on, and the most recent stuff on it is from 2015. Sketchiness of that particular site aside, though, it sure looks like there isn’t a consensus about what average BG results in what HbA1c %. There are lots of charts out there, and they generally don’t seem to agree with each other. Does anyone know why that would be?

@srozelle , since glycolated hemoglobin or Hemoglobin A1c came into use 1975 / 1976 [I was part of the study] there have been differences - HgA1c, HbA1c laboratory tests that use blood from a vein, and now the finger-stick that uses capillary blood; all three can give varying results. Up until about the mid 1990s, there were two lab test styles, one with a “neutral point” of 6.5? and the other with a “neutral point” of 6.0% that indicated average BG close to 120 mg/dl which was determined to be ideal for a person with diabetes. The HbA1c with the 6.0% base is now the standard. There are still conversion charts around that reflect the older type test.

I’m still skeptical about the finger-stick A1c. I’ve had the finger-stick done three times by professionals during the same week when I had a lab-test HbA1c - the comparative results have differed by as much as a full percent - the fingerstick always lower. The ADA calculator at the link you posted provides the same result as the chary I have here on my desk - the chart is based on National Institute of Health [NIH] study data released in 2018.

This is great information, Dennis, as always. I guessed it had to be something like that, but I did not guess you’d have personal knowledge! :sunglasses: Thank you for being here and sharing with the rest of us!