Insulin Sensitivity Factor (ISF) indicates how much one unit of rapid or regular insulin will lower blood glucose (mg/dll or g/mol).

The correction factor, is the calculation to determine the dose of insulin necessary to correct the glycaemia.

The insulin sensitivity factor may vary and be different from one time of day to another even it is possible that significantly varies between disease stages.

When to use insulin correction factor?

Correction factor applies in two situations:

  1. When having a high glycemia before meals (hyperglycemia). It is essential to know the amount of insulin that is needed, since even having into account the amount of carbohydrates that will be ingested, it is also necessary to have into account and correct the excess of initial blood glucose. Therefore, if the insulin dose is injected only having into account the amount of carbohydrates, the glycemia will remain high after a meal. That is why it is required to know the insulin sensitivity factor and apply it.
  2. When having a high blood glucose two hours after eating (hyperglycemia).

How to calculate your insulin sensitivity factor

For its calculation, it is used the total daily insulin dose(both rapid and slow acting insulin, if both are used).

Choose one or the other rule depending on the type of insulin that is used:

  • Ultra rapid acting insulin: Use the 1800 rule. This is done by dividing 1800 by the total daily dose.
  • Rapid acting insulin: Use the 1500 rule. This is done by dividing 1500 by the total daily dose.

WARNING: It is mandatory to have into account the need to let run a certain time between meals, since if something is ingested during the 2 hours after the previous meal and it is performed an injection again, the body keeps the effects of the previous injection of rapid acting insulin.

To better control the amount of carbohydrates it is advisable to avoid eating out, banquets or feasts during those days, as well as lead a normal and routine life.


Total daily insulin dose

Example: A patient daily uses 30 units of Toujeo basal insulin and 16 units of ultra rapid insulin of Humalog, that is to say, a total of 46 units of daily insulin doses.

His/her insulin sensitivity factor would be calculated by 1800/46 = 39

The insulin sensitivity factor is 39, in other words, each insulin unit lowers blood glucose in 39 mg/dl


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How to use insulin sensitivity factor to calculate the bolus corrector

Once we know the insulin sensitivity factor we may calculate the correction dose when the blood glucose levels are not within the target range. Before the calculation, it is necessary to know the glycemia target range, since this is different for each person. The average range usually is 80-140 mg/dl.


Calculation of extra insulin to inject


A patient has a glycemia of 257 mg/dl and his/her glycemia target is 90 mg/dl with an insulin sensitivity factor of 39.

It has to be applied the formula 257-90/39 = 4,2 extra units to administer as correction dose.

How to calculate insulin ratio

Insulin ratio is the amount of rapid insulin needed for each portion of carbohydrates (10gr or 15 gr).

To get this information it is necessary to previously know the habitual rapid insulin dose and the amount of carbohydrates ingested on each meal. If you do not know how to caltculate carbohydrates protions, we invite you to read this article about counting carbohydrates.

To perform the calculation it is applied a rule of three.


If we take 3 portions of carbs for dinner and we inject 3 units of rapid acting insulin.

For a portion of carbs we will inject x units of rapid acting insulin.

X = 3*1/3 = 1 insulin unit for 1 portion of carbs.


* This guide is a mere orientation that we have designed based on empowered patients’ experience. We advise you to always visit your medical service for solving your doubts, since the opinion of a physician will be more trustable and will be adapted to your personal case.

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By attaching Insulclock to your disposable insulin pen, you will be able to automatically register all data related to your insulin pen. You will always know if you have taken your insulin, how many units and what type of insulin.

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