The drop in blood glucose level, measured in milligrams per deciliter (mg/dl), caused by each unit of insulin taken. Knowing their insulin sensitivity factor can help people with Type 1 diabetes to determine the dose of short-acting or rapid-acting insulin to take.
Health-care professionals use the “1500 rule” to calculate insulin sensitivity factor for people who use Regular (short-acting) insulin. The 1500 rule works as follows: Divide 1500 by the total daily dose of Regular insulin, in units. For example, if a person’s total daily dose is 30 units of Regular insulin, his insulin sensitivity factor would be 50 (1500 ÷ 30). So one unit of Regular insulin would be estimated to lower his blood glucose by 50 mg/dl.
Health-care professionals use the “1800 rule” to calculate insulin sensitivity factor for people who use the rapid-acting insulin analogs lispro (brand name Humalog), aspart (NovoLog), and glulisine (Apidra). This is done by dividing 1800 by the total daily dose of rapid-acting insulin. If the total daily insulin dose is 40 units, the insulin sensitivity factor would be 1800 divided by 40, or 45.
Insulin sensitivity factor can be calculated only for people with Type 1 diabetes. It cannot be calculated reliably for people with Type 2 diabetes, whose pancreases often still make some insulin and who have varying degrees of insulin resistance.