How to test and set ICR, CF and ISF

@Michel how did you go about calculating the new ratios, or did you just do.a.swag with incremental changes? I am currently finding myself in the unusual situation of having to recalculate ICR, ISF, and duration after an extended time period. The last time I calculated the parameters I used current vales and measured changes, which got me close. It would be nice to actually do it correctly this time, especially since I plan to make these changes 1.5 months prior to next Endo visit and would like to have at least a 2week period of demonstrated stability prior to visit.


I am sure @Michel has a great way of doing it. For us, we use a mistake i.e. a flat 200 or 300 to calculate our CF. We give enough insulin to correct the high, but not enough to make us go low, then avoid food until the insulin action has leveled off. It is important for us to do this at both 200 and 300 since we have enough hormone highs and understanding insulin resistance at the higher value is important for treatment decisions.

We don’t explicitly test for ICR anymore, we just Eric’s approach which is whenever he is presented with a difficult meal he will just give a bit more insulin than he should and eat his way out of things. This works well for someone who isn’t worried about weight gain.


I think if I had the metabolism to support that, tighter control would be a lot easier, since I wouldn’t be as worried about going low, especially with a CGM, since easy enough to head it off with some carbs. I’d probably be similarly a bit more aggressive with daytime basal, especially if I were using a pump or an MDI approach where daytime and nighttime could be set differently.


I’m thinking @Michel might be traveling presently and hasn’t seen this. But I asked @Chris to split the thread because I think we could use some instructions about how to test and set these.

I remember showing up here at FUD and having no idea what all the acronyms meant (and I had to do some research to make sure I wasn’t totally wrong while writing this post)!

ICR (insulin to carbohydrate ratio) is defined as the number of grams of carbohydrate that are covered/disposed of by 1 insulin unit. Source

CF (Correction Factor - sometimes called Insulin Sensitivity Factor/ISF), is how much 1 unit of rapid acting insulin will generally lower your blood glucose over 2 to 4 hours when you are in a fasting or pre-meal state. Source

Duration of Insulin Action (DIA) is another term that is helpful when trying to determine how long your insulin is working to lower BG. It refers to how long from the time of injection until the insulin is out of your system. Source

So, how do folks determine these things for themselves? Do they follow the general instructions? Is there a trick?