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How to Calculate ISF

Updated March 23, 2017

Insulin Sensitivity Factor (ISF), is defined as the drop in blood glucose level, measured in milligrams per decilitre (mg/dl), caused by each unit of insulin taken. This formula is used by people with type 1 diabetes to determine the correct dose of either short-acting or rapid-acting insulin that they should take at any given time. Diabetics who use short-acting insulin calculate their ISF using the 1,500 rule, which means they divide 1,500 by their total daily dose of insulin. Similarly, diabetics who use rapid-acting insulin calculate their ISF using the 1,800 rule, which means they divide 1,800 by their total daily dose of insulin.

Go to the official OB Focus website.

Click "Calculators" on the home page.

Click "Insulin Sensitivity & Carbohydrate Ratio Calculator."

Fill out the information required for the calculator including: your total daily dose of insulin in units, your sensitivity constant, your current blood glucose in mg/dl, and your target blood glucose in mg/dl. Your total daily dose of insulin in units refers to how many units of insulin you're currently taking each day. Your sensitivity constant is determined by the type of insulin you use. If you use short-acting insulin, your sensitivity constant is 1,500, and if you use rapid-acting insulin, your sensitivity constant is 1,800. Your current blood glucose level refers to the reading of your last test, and your target blood glucose level is the level your physician told you to aim for.

Click "Calculate."

Review your results. The ISF calculator will tell you how many mg/dl your blood glucose level is decreased by one unit of insulin, and also how many units of insulin are needed to correct your current dose.

Tip

Always consult with your doctor before altering your doses.

Warning

ISF calculations only work for type 1 diabetes and not type 2.

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