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. It helps move blood glucose (blood sugar) from your bloodstream into your cells where it's used for energy. Glucose comes from many foods you eat. It's your body's main source of energy.

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

• Blood glucose levels increase after you eat.
• When blood glucose rises, your pancreas releases more insulin into your blood.
• The insulin lets glucose get into your cells, which lowers your blood glucose level.
• When your blood glucose level returns to a range that's normal for you, your insulin levels decrease, too.

Serious problems can develop if your pancreas doesn't make the right amount of insulin at the right time. For example:

• If your pancreas makes too much insulin, you may have too little glucose in your blood. 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 makes too little insulin, glucose can't get into your cells from your blood. The glucose builds up in your bloodstream until your blood glucose level is too high. This is called hyperglycemia. If your blood glucose levels stay high over time, you could develop 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.

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.
• Diagnose insulin resistance. With insulin resistance, your cells don't respond well to insulin and can't easily take in glucose from your blood. Your pancreas may 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 wear out and stop making enough insulin. This can lead to prediabetes, which means your blood glucose levels are higher-than-normal, but not high enough to be diabetes. If blood glucose levels keep increasing, you can develop type 2 diabetes.
• Guide treatment decisions for type 2 diabetes. An insulin test may be used to decide if a person with type 2 diabetes needs to take insulin as part of their diabetes treatment.
• To monitor how well pancreatic islet cell transplantation surgery is working. This surgery is used in people who have type 1 diabetes. Type 1 diabetes is an autoimmune disease that destroys the special islet cells in the pancreas that make insulin.

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 (low blood glucose). Symptoms of mild to moderate hypoglycemia include:
  • Sweating
  • Feeling shaky or jittery
  • Arrythmia (a problem with the rate or rhythm of your heartbeat)
  • Confusion
  • Dizziness
  • Headache
  • Hunger

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

• Have insulin resistance or have a high risk for developing it. 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)
• Had surgery on your pancreas:
  • To transplant the part of the pancreas that makes insulin (islet cell transplantation). You may need insulin testing to see if the transplant is working properly.
  • To remove an insulinoma. This is a tumor in the pancreas that makes too much insulin and causes low blood glucose. After surgery you may need insulin testing to check whether any tumor tissue is left and to see if the tumor has come back. Insulinomas are uncommon and usually aren't cancer.

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. 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 results of other tests, including a blood glucose test. For example:

• If your insulin level is high and your blood glucose is normal or a little above normal for you, you may have insulin resistance.
• If your insulin level is high or normal and your blood glucose is low for you, you may have hypoglycemia from too much insulin. Possible causes include:
  • A pancreatic tumor (insulinoma)
  • Cushing's syndrome
  • Taking too much insulin for diabetes
• If your insulin level is low and your blood glucose is high for you, it may mean that your pancreas can't make enough insulin. Possible causes include type 1 diabetes and pancreatitis.

There are other possible causes of abnormal levels of insulin and glucose. Ask your provider to explain what your test results say about your health.

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

Is there anything else I should know about an insulin in blood test?

An insulin in blood test is often done with a C-peptide test. Your pancreas releases equal amounts of insulin and C-peptide into your bloodstream at the same time. C-peptide doesn't affect your blood glucose levels, but it stays in your blood longer than insulin. So, measuring C-peptide provides a more accurate way to find out how much insulin your pancreas is making.