Is there a “method” for determining truest insulin sensitivity for knowing correction factor for pump?

Hi, all. This might seem like a dumb question, but since I am on MDI for a bit of a learning time, before going back to the Omnipod five, I am wondering how I might determine my truest correction factor/insulin sensitivity. I guess there could be a method or just making a guesstimate before a correction and figuring it out. But I thought I’d ask first before I reinvent the wheel. Thanks in advance for any help and/or opinions. I am trying to be ready at the get-go when I go back to the pump. I want the OP5, or t-slim, to have good working data from the start.

Good morning, this may help.


Hey, one more, I linked to resources. I use this site allot for reascherch.

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The “rule of 1700” formula that T1john linked to is something that doctors use as a decent starting estimate; it is derived from averages over large populations. Some use “rule of 1800” instead. In my view, the truth of the formula is similar to the truth of the initial estimate for basal from a formula, and neither one is accurate but they are what we have for initial estimates in the absence of actual individual experience. (The initial basal dose estimate is this: divide body weight in pounds by 4 to get an estimate of total daily insulin need, divide that value by 2 to get an estimate of total daily basal, divide that by 24 to get an estimate of hourly basal rate.) For any individual this estimate can be dangerously wrong, so a physician will calculate that number and then give a significantly smaller starting dose for safety, and gradually increase until enough insulin is given without causing hypoglycemia.

But to find the actual value of insulin sensitivity for your individual body you would have to run the experiment. You need a period of about 4 to 6 hours where your BG would stay steady around 120. That means the basal is right, there’s no leftover IOB from a meal bolus, no food being digested, no particular stress or exercise to push your BG around. Then take a correction that you would expect to lower your BG from 120 to 100, and watch what happens over the next 4 to 6 hours. The number of mg/dL that your BG actually drops after the 6 hours is your measured ISF. At that time. You’d repeat the experiment a few times, because so many other things can affect BG. And, by the way, for some people the ISF varies during different times of the day, and many people are somewhat insensitive to insulin during hyperglycemia: 1 unit of insulin doesn’t lower the BG as much as expected.

I find that experiment to be too tedious and demanding, and I just don’t have the discipline anymore to measure it properly. Instead, I adjust my settings by tiny amounts until they work. The order is important. First I get my basal right, so that my BG stays level if I skip or delay a meal. Then I get my insulin:carb ratio right by seeing that my BG about 4 hours after a meal is about where it was before I ate. After both of those numbers are dialed in, then I get my insulin sensitivity factor right by seeing that corrections work properly from modest highs, like 140 or 150 down to 100 in 4 to 6 hours. For each of these three settings in turn, I make very small adjustments and watch what happens to see whether I need to go further or back off a little.


All BG numbers are different. I mean, one particular 120 is not always the same as another 120.

It can be a slowly rising 120, a sharply rising 120, a declining 120, a flat 120. A 120 with some food behind it. A 120 with some insulin behind it. A 120 after waking up, a 120 after exercising. A 120 during different times of the month or times of the day. On and on.

So you can come up with general correction factors all you want. But they may only work correctly at certain times. And other times they won’t.

So how do you know how much insulin to give yourself?

It takes practice and thinking about all of the million things and putting them together and using The Force.

You do it over and over under all of the different BG’s and circumstances and you eventually learn how much insulin to take.

Trying to simplify it all into a certain number of units for a particular BG number is a fine start. But it is only a guideline. The best way to learn it is by doing it over and over. Eventually you just know.


I total agree with both @bkh and @Eric, both linked resources say same, it’s just a startling point.


And having CGM is also helpful!!!

When I started Tandem pump, was surprised at how often my basal is adjusted, but keeps my BG in range.

If I check reports, the Total actual basal by day can vary.


Just a warning. The OP5 has a learning curve that drives people nuts at first. Of course it helps to give it accurate data, but it still will go through it’s learning curve.


@bkh Thanks so much. I appreciate the links from t1John, but definitely am trying to experiment on me. My endo probably used the traditional ways a few years ago upon diagnosis, but I was looking for a rationale and system as you mentioned. The time factor for me, too, is too long and I am more insulin sensitive after morning is over, plus, on mdi, I am limited by .5 increments of insulin, so maybe I will do better to experiment while on manual on the pump. Much to consider. And, geez, thanks for saying some are insulin resistant with hyperglycemia- I have had some periods lately that my .5 corrections seemed to do almost nothing and I began to think that a .5 unit has some sort of room for error since such a small amount and maybe a tiny air bubble was in there (my mind goes wild trying to explain things to myself🤪). I appreciate the detail and the explanation. I am probably seeking more of just some basic plan or understanding to use so I know what to expect and then compare result to expectations and ultimately feel I have a handle on things. Thank you!


@T1john Thanks for this and always being quick to help! I appreciate your references and knowing what is out there. Fills in lots of gaps for me.

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@Eric Wow, Eric! I just responded to bkh in a way that amounts to what you said so succinctly. Experience and The Force!:grin::grin::grin: And I love knowing methods of discovery like bkh said and the order of finding the keys, knowing all the while that adding the layers and layers of experience is what will get to The Force! I am sure I will get there. Thanks!

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@MM2 Thanks! I have had a strange set of wonky dexcoms lately and get 3 month supply at a time, so sometimes wonder if I am getting so e out-of-tolerance boxes of them, but nonetheless, the cgm is the absolute best technology. I am lucky to have been diagnosed when this was available. I actuallt want to try libre 3, but not sure I wouldn’t miss some dexcom features. While on mdi, I can try this, but of course, at present, only dexcom works with pump. Anyway, thanks for the response.

Just a thought, Quadgirl, as a woman, you have a different hormonal cycle that can affect insulin sensitivity or resistance. If you are still in that age set then it is something to consider.

My self with varying degrees of insulin resistance my correction factor is nearly worthless. Since I am using a pump (Tandem) I have learned to override the suggested meal boluses a bit depending upon how BG is trending.

I am fasting for up to an hour after I wake and took thyroid meds. This morning I woke at 105mg/dl. BG rose to 132mg/d. I did a 1u bolus with was .8u more than my pump suggested. This started BG to trend down a bit before I prebolused for my breakfast.

I would like dosing to be set in stone, but that just doesn’t work for me. Some with T1DM that don’t have strong insulin resistance are able to go by their ISF and correction without problems - or so I hear :rofl:


Thanks for that, @CarlosLuis Alas, I am past the hormonal fluctuations (which the name quadgirl, named after my audio hobby, does not do well to convey😜). I appreciate you trying to help me figure things out! Take care.


I probably edited my post while you sent your to add a bit about my own issues with getting accurate CF with varying insulin resistance. My correction factor just doesn’t work well for me.

For those who have more stable insulin sensitivity this method may work well. It’s just not for me.



@CarlosLuis, Yea just had to add I am one of the lucky diabetics, being T1 with insulin resistance. along with gastroparesis and numerous Gastrointestinal issues so it’s all sort of a crapshoot for me.

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This is the best insulin sensitivity explanation I’ve ever had. Thank you for that.

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