How to figure your Insulin Sensitivity Factor Properly?

Spent 3 days in hospital last week due to hypo and migraine headache of 7 days. When I asked about the insulin sensitivity factor on my pump, doc said leave it alone. So I did. Now, I would like to figure it out on my own with a little help. How is this level figured appropiately? Do you have to be 80-120 to figure it or can you be whatever sugar you have? My thought: 1 unit of insulin with no carbs, check BS prior to and every hour up to 4 hours after with no carbs (something of a fast). Am I right or wrong with this way of figuring? I do know that I will have at least four different ISF’s to figure out because I also have 4 different insulin to carb ratios.

Here are 2 articles on how to calculate it. I actually use 1700 instead of 1800 – I think that works better for me and I want to be more aggressive than some people. I had a spreadsheet when I first got my pump so I could easily calculate my TDD and go from there.

The articles Kelly posted will give you a good estimate. Usually elaborate testing is only required when you find the ISF to be completely wrong. It’s usually just a matter of subtle changes up or down through experience. It’s pretty much impossible to get a ‘perfect’ ISF so as long as something works reasonably well then it is fine.

But if you want to test it thoroughly then you want to do it without carbs or any other insulin on board – so wait 4 hours from your last bolus and fast during the course of the test. To start, you should be on the higher end of normal or higher (like 115-150) because you can’t test an ISF if you don’t currently need a correction bolus (or you’ll go low). Start with the ISF your doc gave you or the one calculated above and use it to calculate the full correction bolus and then test to see how close you are to your target over the 3-4 hours. You can determine whether it needs to go up or down based on how far you are from your target at the end, where ISF = (Start BG - End Bg) / Insulin Taken. It’s best not to do this first thing in the morning because you’ll end up fasting for an extended period and that may alter the results of your test. It’s also important that your basal dose is correct or that may also influence the results.

It’s not unusual to have different ISF’s for different times or different activity levels, so you may very well need different ones but you can figure out your base ISF and then make adjustments for different influences as you find them necessary.

Here is another good article on how to test ISF. One way of establishing the proper conditions for an ISF test is to either underbolus for a meal or suspend your basal for a couple hours after a meal. This should cause your blood sugar to be a bit high, you want at least a good 50 mg/dl for ISF testing.

I would refer to the insulin correction factor test in the book “Using Insulin”. You start at least 3.5 hours after your last bolus and meal with a bg of over 200, take 1 unit and fast for the next 4 hours and test once an hour or anytime you feel off. Your four hour reading subtracted from the bg reading you started with would=your sensitivity factor.
(Example: 4 hours after eating my bg is 210 so I take one unit (with no food and fast for 4 hours) and my bg at 4 hours is 160 so that means my sensitivity factor-50 points per unit.)

My ISF has never been figured usefully, I should say, when above 200. So I have tested with it at 180. At 180 I can reliably know from prior experience that 1 unit will drop me 40; 2 units will drop me 80.
Above 200 I find that the ISF is dealing with resistance. At 220, for example, 1 unit drops me 25. At 195, 1 unit drops me 30. And this has happened over and over, so it’s reliable.
The 1800 and 1700 rules have never been reliable with anyone I have worked with; I consider them worthless.
I believe in dealing with small numbers. You definitely need to figure that anyone giving themselves one unit of insulin can drop up to 60. SO, Don’t try it below 160. That gives you a bit more cushion at the bottom.
After you have done that, see what one unit does above 200, to see if you garner resistance up there.
I like to think of ISF as being reliable in the one hundreds and another number entirely in the 200s. Test and retest.

Thanks for the detailed response Leo…interesting…wonder how long after a high you stay insulin resistant.

Thank-you for the help. I am seeing the internist tomorrow as follow-up for hospital discharge. Called Monday and had some of hte readings changed, but not enough though. I think I will be doing the fine tuning myself without assistance except from this forum as most of you have done the figuring with an educated professional or were referred to books by one or more educators. Living in rural America is not always the best, but thank God for computers and helpers online!!! :slight_smile: