What to Know About Insulin Sensitivity Factor

Medically Reviewed by Michael Dansinger, MD on July 07, 2023
4 min read

When you have diabetes, your body has low insulin levels or no insulin at all. Insulin is a crucial hormone that helps in the control of blood sugar and other body processes. Without insulin, your body can’t process glucose the right way and this can lead to diabetes.

There are two forms of diabetes: type 1 and type 2. With type 1 diabetes, your pancreas is unable to make insulin. With type 2, your body can't use the insulin your body makes properly. Taking insulin is necessary in both cases.

You need insulin injections to keep your blood sugar at normal levels. At first, it may be hard to understand the right amount of insulin you need. You will need some calculations to get the dosage right, and the insulin sensitivity factor can help you do that.

The insulin sensitivity factor refers to the drop in blood sugar level. This measurement is done in milligrams per deciliter (mg/dl) and depends on the units of insulin taken. While insulin is meant to help your blood sugar levels fall, they should not fall too far as this can also be risky. Knowing your insulin sensitivity factor enables you to determine the dose you need for short-acting or rapid-acting insulin

It’s crucial to get your insulin factor right for two reasons. First, if you take a high dose that makes your blood sugar drop too low, you may develop hypoglycemia. This happens when the blood sugar levels fall below 70 milligrams per deciliter. The condition is dangerous and can lead to seizures or loss of consciousness.

Second, if you take a dose of insulin that's too low, it may not help stabilize your glucose levels. The result is a condition known as hyperglycemia, which can cause severe complications over time. These complications can have adverse effects on your:

  • Eyes
  • Kidneys
  • Nerves
  • Heart and other organs

Insulin sensitivity differs from one person to another, which is why you need to know the correct dose to take. In general, diabetes type 1 has a higher insulin sensitivity than type 2 diabetes. Your insulin sensitivity also tends to vary during the day depending on how active you are and your hormone secretion. When you're sick, your insulin sensitivity also tends to change.

There are two ways to calculate your insulin sensitivity factor. One method will help you determine your sensitivity to regular insulin, and the other will help you know your sensitivity to short-acting insulin.

Regular insulin. Regular insulin is a synthetic hormone that the body uses to process sugar that enters the bloodstream as part of the digestive process. It starts working within 30 minutes to an hour after intake, and it takes about two to four hours before the medication achieves maximum effectiveness. The effectiveness lasts for six to eight hours. Regular insulin comes in three forms:

  • An injectable solution
  • An inhalable powder
  • An intravenous solution

To calculate your insulin sensitivity factor for regular insulin, use the “1500 rule.” It will help you know how much your blood sugar will drop per unit of regular insulin. For example, if your recommended daily dose of regular insulin is 30 units, divide that into 1500 to get 50. The interpretation is that your insulin sensitivity factor is 1:50. This means that one unit of regular insulin lowers your blood sugar levels by about 50 milligrams per deciliter.

Short-acting insulin. This type of insulin takes a shorter time to affect your glucose levels than regular insulin. It begins to work within 30 minutes, which means you should take the injection 30 minutes before taking a meal. The insulin reaches its maximum effect two to five hours later and can last for as long as six to eight hours.

Calculating the insulin sensitivity factor of short-acting insulin is based on the “1800 rule.” If you take 30 units daily of the short-acting insulin, divide that into 1800. The result is 60, which means that you have an insulin sensitivity level of 1:60. One unit of short-acting insulin will decrease the amount of sugar in your blood by about 60 milligrams per deciliter.

Your insulin levels change during the course of the day for many reasons. It's essential to choose the right time to test the factor for the most accurate results. Doctors recommend checking your insulin sensitivity factor when:

  • Your blood glucose level rises at least 50 milligrams per deciliter above the target level.
  • You haven't had a meal for four hours.
  • You predict that you will not eat for more than four hours.
  • You haven't taken a bolus insulin dose for a minimum of four hours.

Don’t test for the insulin sensitivity factor when:

  • You’ve had periods of low blood sugar levels.
  • You’re sick or have an infection.
  • You've undergone strong, physical activity.
  • You’re emotionally stressed.

Show Sources


AIP Conference Proceedings: “Assessing the impact of inaccurate insulin-to-carbohydrate ratio on the patient's glycemic targets and lifestyle management.”

Annals of Internal Medicine: “Medicines for Treatment Intensification in Type 2 Diabetes and Type of Insulin in Type 1 and Type 2 Diabetes in Low-Resource Settings: Synopsis of the World Health Organization Guidelines on Second- and Third-Line Medicines and Type of Insulin for the Control of Blood Glucose Levels in Nonpregnant Adults With Diabetes Mellitus.”

Better Health Channel: “Diabetes and Insulin.”

Clinical Diabetes: “Insulin Therapy.”

Current Diabetes Reports: “A Review of Insulin-Dosing Formulas for Continuous Subcutaneous Insulin Infusion (CSII) for Adults with Type 1 Diabetes.”

Diabetes Education Online: “Types of Insulin.”


Diabetes Technology Therapeutics: “Insulin Sensitivity Index-Based Optimization of Insulin to Carbohydrate Ratio: In Silico Study Shows Efficacious Protection Against Hypoglycemic Events Caused by Suboptimal Therapy.”

Indian Journal of Endocrinology and Metabolism: “Assessment of insulin sensitivity/resistance.”

Journal of Diabetes Science and technology: “Bolus Calculator Settings in Well-Controlled Prepubertal Children Using Insulin Pumps Are Characterized by Low Insulin to Carbohydrate Ratios and Short Duration of Insulin Action Time.”

JOURNAL OF DIABETES SCIENCE AND TECHNOLOGY: “Guidelines for Insulin Dosing in Continuous Subcutaneous Insulin Infusion Using New Formulas from a Retrospective Study of Individuals with Optimal Glucose Levels.”

Mouri M. and Badireddy M. Hyperglycemia, StatPearls Publishing, 2021.

Munguia C. Regular Insulin, Statpearls Publishing, 2020.

National Institute of Diabetes and Digestive and Kidney Disease: “What is Diabetes?”

The American Journal of Medicine: “Hypoglycemia.”

THE CLINICAL BIOCHEMIST REVIEWS: “Insulin and Insulin Resistance.”

The Journal of Clinical Endocrinology & Metabolism: “Insulin sensitivity and Its Measurement: Structural Commonalities among the Methods.”

Transitional Pediatrics: “Type 1 Diabetes: where are we in 2017?”

Vascular Health and Risk Management: “Inhaled Insulin: Overview of a novel route of insulin administration.”

View privacy policy, copyright and trust info