Insulin in Blood Test

What is an insulin in blood test?

An insulin in blood test measures the amount of insulin in a sample of your blood. Insulin is a hormone that your pancreas makes. Hormones are chemical messengers in your bloodstream that control the actions of certain cells or organs.

Insulin helps control the amount of glucose (blood sugar) in your blood. Glucose is your body's main source of energy. You get it from many of the foods you eat. 

Normally, insulin and blood glucose levels rise and fall together:

• After you eat, your blood glucose level increases
• The increase in blood glucose tells your pancreas to release more insulin into your blood
• Insulin helps glucose move from your blood into your cells, where it can be used for energy
• As your blood glucose level decreases, your pancreas releases less insulin

Problems can develop if your pancreas makes too much or too little insulin or if your cells don't respond well to insulin. For example:

• If you have too much insulin in your blood, your blood glucose may become too low. This is called hypoglycemia. If blood glucose levels drop to a very low level (severe hypoglycemia), your brain cells may not get enough glucose to work properly. This is a serious condition that needs medical treatment right away.
• If your pancreas doesn't make enough insulin or if your body doesn't respond well to insulin, glucose can't get into your cells from your blood. The glucose then builds up in your bloodstream, causing your blood glucose levels to be too high for you. This is called hyperglycemia. Over time, high blood glucose can lead to type 2 diabetes, which can cause serious complications in your eyes, heart, and other parts of your body.

If you have signs or symptoms of a health condition related to insulin, an insulin in blood test can help check how much insulin your pancreas is making. However, an insulin in blood test is not usually used to diagnose diabetes. That's because people with diabetes may have insulin levels that vary between what is healthy for them and what is below or higher than their usual range. So, providers usually diagnose diabetes with tests that measure your blood glucose.

Other names: fasting insulin, insulin serum, total and free insulin

What is it used for?

An insulin in blood test may be used with other tests to help:

• Find out the cause of hypoglycemia (low blood glucose). This is the main reason for doing insulin testing.
• Help evaluate how much insulin your pancreas is making. In certain situations, your provider can use the results of these tests to help make decisions for your diabetes treatment.
• Help diagnose an insulinoma, an uncommon, benign (noncancerous) tumor of the pancreas that makes insulin. Too much insulin from the tumor can cause low blood glucose. They are usually removed during surgery.
• See if an insulinoma has come back after surgery.
• Monitor how well pancreatic islet cell transplantation is working. This surgery is used in people with type 1 diabetes. Type 1 diabetes is an autoimmune disease that destroys the special islet cells in the pancreas that make insulin. These tests can help see if the transplanted cells are making insulin. 

In many cases, your provider will use other tests along with an insulin in blood test. The most common of these are:

• C-peptide tests. Your pancreas makes C-peptide when it makes insulin. However, C-peptide stays in your blood longer than insulin does and isn't found in insulin medicine. So, measuring C-peptide along with your insulin levels can help your provider get a clear idea of how much insulin your pancreas is making.
• Fasting blood glucose tests. These tests measure how much glucose you have in your blood after fasting (not eating or drinking) for a certain period of time.
• A1C tests. This test measures the average amount of glucose in your blood over the course of a few months.

Providers can also use a combination of these tests to diagnose and monitor treatment for various conditions, including insulin resistance. 

Insulin resistance is a condition in which your body doesn't respond to insulin the way it should. When this happens, your cells can't easily take in glucose from your blood. Your pancreas may then make more insulin to help glucose get into your cells. This can keep your blood glucose in a healthy range for a while. But over time, your pancreas may not be able to make enough insulin to keep your glucose in a range that's healthy for you. This can lead to prediabetes and type 2 diabetes.

Why do I need an insulin in blood test?

You may need an insulin in blood test if you:

• Had a blood glucose test that showed you have low blood glucose levels
• Have symptoms of hypoglycemia
• Have insulin resistance or a high risk for developing it
• Had pancreatic islet transplantation surgery or surgery to remove an insulinoma

Symptoms of mild to moderate hypoglycemia include:

• Sweating
• Feeling shaky or jittery
• Irregular heartbeat (Arrhythmia)
• Confusion
• Dizziness
• Headache
• Hunger

Severe hypoglycemia can cause fainting and seizures. This serious condition needs medical treatment right away.

Your risk for insulin resistance is higher if you have:

• Prediabetes
• Type 2 diabetes
• Polycystic ovary syndrome (PCOS)
• Heart disease
• Acanthosis nigricans (dark, thick, velvety skin around the neck or armpits)

What happens during an insulin in blood test?

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.

Will I need to do anything to prepare for the test?

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. This is because some people who take insulin can develop antibodies against insulin. Antibodies are proteins your immune system makes to fight disease-causing germs, such as viruses and bacteria. These antibodies can interfere with insulin tests and cause inaccurate results. Tell your provider if you take any insulin medicines. But don't stop taking any medicines without talking with your provider first.

Are there any risks to the test?

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.

What do the results mean?

To understand what your insulin test results mean, your provider will consider your medical history and the results of other tests.

In general:

• 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.
• 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. Your provider may order other tests, such as C-peptide or proinsulin, to help find the cause. Possible causes include an insulinoma, Cushing's syndrome, or taking more insulin than your body needs.
• 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. 

Reference ranges can vary between laboratories, and some insulin tests measure certain types of insulin medicine differently.

If your test results are not in the usual range, it doesn't always mean that you have a medical condition that needs treatment. 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.

Learn more about laboratory tests, reference ranges, and understanding results.