Insulin in Blood
Reviewed
Also called: Fasting Insulin, Insulin Serum, Total and Free Insulin
An insulin in blood test measures the amount of insulin in a sample of your blood. Insulin is a hormone that your pancreas makes.
Specimen: Blood
Urgent safety information
Severe hypoglycemia can cause fainting and seizures. This serious condition needs medical treatment right away.
Why this test may be ordered
- To help find out the cause of hypoglycemia (low blood glucose).
- To diagnose insulin resistance.
- To guide treatment decisions for type 2 diabetes.
- To monitor how well pancreatic islet cell transplantation surgery is working.
- To check after surgery to remove an insulinoma.
Preparation and collection
Your health care provider will tell you how to prepare for an insulin in blood test. You will probably need to fast (not eat or drink) for 8 to 12 hours before the test. If you take biotin supplements (vitamin B7), or supplements that include biotin, you'll need to stop taking them for at least a day before your test. Insulin medicines may also affect the accuracy of an insulin in blood test. Tell your provider if you take any insulin medicines. But don't stop taking any medicines without talking with your provider first.
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
If a result or symptoms suggest an emergency, get emergency medical help right away.
To understand what your insulin test results mean, your provider will consider your medical history and the results of other tests.
- High insulin with normal or slightly high blood glucose: If your insulin level is high and your blood glucose is normal or a little above normal for you, your body may be making extra insulin because your cells aren't responding to it normally. This can happen with insulin resistance. Limitation: Reference ranges can vary between laboratories, and some insulin tests measure certain types of insulin medicine differently. Next step: So, an insulin result is usually not enough by itself and you may need other tests.
- High or normal insulin with low blood glucose: If your insulin level is high or normal and your blood glucose is low for you, it may mean that you have hypoglycemia from too much insulin. Possible causes include an insulinoma, Cushing's syndrome, or taking more insulin than your body needs. Limitation: Insulin levels vary depending on your blood glucose level. Next step: Your provider may order other tests, such as C-peptide or proinsulin, to help find the cause.
- Low insulin with high blood glucose: If your insulin level is low and your blood glucose is high for you, your pancreas may not be making enough insulin. Possible causes include type 1 diabetes and pancreatitis. Limitation: If your test results are not in the usual range, it doesn't always mean that you have a medical condition that needs treatment. Next step: To understand what your insulin test results mean, your provider will consider your medical history and the results of other tests.
- If you take biotin supplements (vitamin B7), or supplements that include biotin, you'll need to stop taking them for at least a day before your test.
- You will probably need to fast (not eat or drink) for 8 to 12 hours before the test.
What to do next
Insulin levels vary depending on your blood glucose level. So, an insulin result is usually not enough by itself and you may need other tests.
- What do my insulin and blood glucose results mean together?
- Do I need any other tests, such as a C-peptide test?
- What is my risk for insulin resistance or diabetes?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.