Insulin sensitivity factor

Hi. I’m new to the group and have been pumping with the animas ping for about a month. I was wondering if anyone had any issues with the insulin sensitivity factor when doing a correction bolus. I find that whenever I do one my blood sugar goes low. I know there is a mathematical way to calculate it based on the number of units you take per day but does anyone know how you can calculate it based on something other then math? Thanks!

Sorry, I don´t know a way to do it without math. But maybe this from the makers of RapidCalc will help. RAI is rapid acting insulin:

Correction Factor : Blood Glucose Drop per unit of insulin
The most common approach is to use the “rule of 100” which entails dividing the Total Daily Dose (TDD) into 100 to give the blood glucose drop in mmol/L. For those who use mg/dL to measure BGL, the rule is expressed as the “rule of 1800”.

To give an example: If a person is on a TDD of 50 units then 1 unit of RAI should drop their BGL by 100/50 = 2 mmol/L or using mg/dL this would be expressed as 1800/50 = 36 mg/dL.

For most Type 1 adults 1 unit of RAI will drop BGLs by between 2-3 mmol/L (36-54 mg/dL) but for people on lower TDDs, 1 unit of RAI will achieve even greater drops of BGLs. Using the “rule of 100” a person on a TDD of 10 units should find that 1 unit of RAI will drop their BGL by 10 mmol/L (180 mg/dL). Paediatric patients tend to be more sensitive to insulin and the BGL drop per unit of insulin can be significantly greater than the ranges shown above.

Just as carb ratios can vary throughout the day, you should not be surprised if your correction factor varies, as the same factors are at play.

To test your correction factor:-

Ensure your BGLs are within range and stable (not rising/falling or being influenced by exercise, stress, recent hypos, food, IOB etc)
Test your BGL and if it is above your target BGL.
Inject your calculated correction dose of RAI.
Do not eat again or do anything that will significant affect your BGL.
Test your BGL every hour for the next six hours.
The drop in BGLs to your target BGL within this time period should verify whether you have the right correction dose.

Hi Melissa,

To determine your Insulin Sensitivity Factor (ISF) without using a bunch of math, I recommend you do a ISF test as described in the bible of Insulin pumping by John Walsh. Basically you do the following:

Make sure your basal rate is consistent before hand- so there are no unexpected rises or falls. If that is the case, then eat something with a hefty amount of carbs in it- so that your blood sugar will rise to about 250. Wait an hour to let it level off.

then, make a note of your blood sugar, and do an EZbg bolus according to your set ISF. Test your blood sugar every hour for the next 6 hours. If you return to goal after 4-6 hours and it stays that way, then your ISF is appropriate. If you go low, you need to increase your ISF, if you are higher than goal, you need to decrease your ISF.

For example:
If your ISF is 1:100 and you bolus and go low, try adjusting it to 1:110.
If your ISF is 1:100 and you bolus and are high, try adjusting it to 1:90.

In general, I never adjust mine more than + or - 10. Then I retest on another day and see how that affects it.

I hope this helps. Also, John Walsh has many excellent books out about insulin pumps which I cannot recommend highly enough.


Personally, I find all the formulas approximate at best. The simplest way to tweak your ISF is based on trial and error. You already know your current ISF makes you go low so start by raising that. If you are using 1:60 then try using 1:70. When you are high give yourself a correction and see how you do at around 3 hours. Keep records. If it is bringing you down reasonably within that length of time it is right. If you are still low go to 1:80; if high take it down to 1:65. You want to get close to your goal in 3 hours, 4 at the most. Six hours is too long to stay high and indicates you need more insulin.

Sorry, but you do have to use math to calculate a number - LOL. The insulin sensitivity factor is how much your BG will go down if you take 1 unit of insulin. Of course, this is not a constant number, but to keep things simple, that is what you input. Then you adjust as needed as Lane described above.

Thank you all for your responses. Right now my sensitivity factor is set as 1:40, yet if i calculate using the 1800 rule, it should be more like 1:80, so ill try to increase it and continue increasing it until I find the right factor.

Zoe is right! There are a couple of other issues on ISF. Some, but not all, include: emotional state, activity level before and after, illness, other stressors, and the list goes on.

I ate the same fast food three days in a row at the same time and had three different results: on target, high, and then low. Discussed this with my CDE, the Animas clinical manager, and the Dexcom clinical manager. All three nurses reminded me DM management is still not an exact science. One even shared, use the SWAG theory - Scientific Wise Axx Guess. All I did was grin and start swaging.

Also, my ISF varies for different times of the day. During the 10a to 4p, I use 1:40 while evenings and overnight it is 1:25. GRIN