How to Determine Your Insulin Sensitivity Factor

Medically reviewed by Graham Rogers, MD on May 11, 2016Written by Mary Love on May 11, 2016

Overview

For many people with diabetes, insulin injections are the key to keeping their blood sugar at normal levels. Getting the right amount of insulin can seem a bit tricky at first. This is where you’ll need to do some math to get the dose just right.

The pancreas makes the hormone insulin. Insulin helps the body use sugar as an energy source. It also helps balance your blood glucose levels.

People with type 1 diabetes don’t make enough insulin. People with type 2 diabetes don’t properly use the insulin their bodies make. Taking insulin is necessary for people with type 1 diabetes, but it can also be important for people who have type 2 diabetes.

Why is it so important to get the right amount of insulin?

An insulin dose that’s too high could lower your blood sugar too much. This can cause hypoglycemia. Hypoglycemia occurs when your blood sugar falls below 70 milligrams per deciliter (mg/dL). Hypoglycemia can lead to a loss of consciousness and seizures.

Learn more: Humalog vs. NovoLog: Important differences and more »

An insulin dose that’s too low may not bring your blood sugar to the target level. The resulting high blood sugar is called hyperglycemia. Hyperglycemia can lead to serious complications over time that can affect your:

  • heart
  • kidneys
  • eyes
  • nerves
  • other organs

You’ll need to know how sensitive you are to insulin to know the right dose of insulin to take. In other words, you’ll need to know how much insulin you need to lower your blood sugar by a certain amount.

Insulin sensitivity isn’t the same for everyone. Some people with diabetes are more sensitive to insulin that others. In general, people with type 1 diabetes are more sensitive to insulin than people with type 2 diabetes. Your sensitivity to insulin can vary during the day based on your level of activity and your body’s rhythm of daily hormone secretion. Illness can also affect your insulin sensitivity.

You can figure out your sensitivity to insulin by finding your insulin sensitivity factor.

What is the insulin sensitivity factor?

The insulin sensitivity factor tells you how many points, in mg/dL, your blood sugar will drop for each unit of insulin that you take. The insulin sensitivity factor is also sometimes called a “correction factor.” You need to know this number to correct a blood sugar level that’s too high.

How can you find your insulin sensitivity factor?

You can calculate your insulin sensitivity factor two different ways. One way tells you your sensitivity to regular insulin. The other tells you your sensitivity to short-acting insulin, such as insulin aspart (NovoLog) or insulin lispro (Humalog).

Read more: The effects of low blood sugar on the body »

Regular insulin

For regular insulin, use the “1500 rule.” This tells you how much your blood sugar will drop for each unit of regular insulin.

For example, if you take 30 units of regular insulin daily, divide 1500 by 30, which equals 50. This means your insulin sensitivity factor is 1:50, or that one unit of regular insulin will lower your blood sugar by about 50 mg/dL.

Short-acting insulin

For short-acting insulin, use the “1800 rule.” This tells you how much your blood sugar will drop for each unit of short-acting insulin.

For example, if you take 30 units of short-acting insulin daily, divide 1800 by 30, which equals 60. This means your insulin sensitivity factor is 1:60, or that one unit of short-acting insulin will lower your blood sugar by about 60 mg/dL.

How do you determine insulin dosage?

Once you know how sensitive you are to insulin, you can figure out how much insulin you need to give yourself to lower your blood sugar by a certain amount.

For example, if your blood sugar is 200 mg/dL and you’d like to use your short-acting insulin to lower it to 125 mg/dL, you’d need your blood sugar to drop by 75 mg/dL.

From the insulin sensitivity factor calculation, you know that your short-acting insulin sensitivity factor is 1:60. In other words, one unit of short-acting insulin lowers your blood sugar by about 60 mg/dL.

How much insulin do you then need to lower your blood sugar by 75 mg/dL?

You’ll need to divide the number of mg/dL you want to lower, which is 75, by the number from your insulin sensitivity factor calculation, which is 60. The answer of 1.25 tells you that you need to take 1.25 units of short-acting insulin to lower your blood sugar by 75 mg/dL.

These are rough calculations that mainly people with type 1 diabetes use. If you have type 2 diabetes, you’ll need to check with your doctor for guidance.

Where can you get more help with this if you need it?

If you like using your smartphone, you can use an app to help you calculate your insulin sensitivity factor and dosage. Search for insulin sensitivity or insulin correction calculators on your iPhone or Android device. Find one that seems easy to use and play around with it until you feel comfortable.

You may also be able to find online resources, such as the American Association of Diabetes Educators website, or you can ask your doctor for help.

Takeaway

Understanding your insulin sensitivity is important for maintaining your blood sugar. You can determine this using a mathematical formula. Apps can also help.

Using this method only applies to decreasing your blood sugar when it’s already high. Ideally, these formulas wouldn’t be necessary, but the reality is that there will be times when your blood sugar will be too high. This method can help you safely bring down your blood sugar to a more reasonable level.

The best way to manage your diabetes is to try to keep your blood sugar from spiking. You can accomplish this by using long-acting insulin once or twice per day, and shorter-acting insulin before each meal. This method will involve counting your carbohydrates at meals and dosing your pre-meal insulin based on your individual correction factor.

Apps and online calculators can help you determine your correction factor. You should, however, work closely with your doctor to set up your insulin regimen. You’ll decrease your risk of complications from diabetes by controlling your blood sugar.

You should check your blood sugar after taking extra insulin to make sure that your blood sugar drops appropriately. If you’re using regular insulin, you’ll need to recheck your blood sugar after three hours. That is when it’s effectiveness peaks. You only have to wait 90 minutes to test your blood sugar after using a short- acting insulin.

If your sugar is still too high when you recheck it, you may give yourself another dose based on one of the formulas. If your sugar is too low, you should have a snack or juice. If you’re still having difficulty determining your dosage, ask your doctor for help.

CMS Id: 103553