About the Test
Purpose of the test
An insulin test is a blood test used to measure the insulin levels being produced in your body. It is primarily used in one of the following ways:
- Diagnose an insulinoma, verify that removal of the tumor has been successful, and/or monitor for recurrence
- Diagnose the cause of hypoglycemia in an individual
- Identify insulin resistance
- Monitor the amount of insulin produced by the beta cells in the pancreas (endogenous); in this case, a C-peptide test may also be done.
- Determine when a type 2 diabetic might need to start taking insulin to supplement oral medications
- Determine and monitor the success of an islet cell transplant intended to restore the ability to make insulin by measuring the insulin-producing capacity of the transplant
Testing for insulin may be ordered with glucose and C-peptide tests. Insulin levels are also sometimes used with the glucose tolerance test (GTT). In this situation, blood glucose and insulin levels are measured at pre-established intervals to evaluate insulin resistance.
What does the test measure?
This test measures the amount of insulin in the blood — a hormone produced and stored in the beta cells of the pancreas. It is secreted in response to elevated blood glucose following a meal and is vital for transporting and storing glucose, the body’s main energy source. Carrying glucose from the blood to cells, insulin helps regulate blood glucose levels and has a role in lipid metabolism.
Insulin and glucose blood levels must be in balance. After a meal, carbohydrates usually are broken down into glucose and other simple sugars. These are absorbed into the blood, causing the blood glucose level to rise and stimulating the pancreas to release insulin into the blood. As glucose moves into cells, the level in the blood decreases, and the release of insulin by the pancreas decreases.
If an individual cannot produce enough insulin, or if the body’s cells resist its effects (insulin resistance), glucose cannot reach most of the cells, and they starve. Meanwhile, blood glucose rises to an unhealthy level. This can cause disturbances in normal metabolic processes, resulting in various disorders and complications, including kidney disease, cardiovascular disease, and vision and neurological problems.
When should I get this test?
Insulin levels are most frequently ordered following a low blood glucose test result and/or when someone has acute or chronic symptoms of low blood glucose (hypoglycemia) caused by, for example, an insulinoma. Symptoms of hypoglycemia may include:
- Blurred vision
- In serious cases, seizures and loss of consciousness
These symptoms may indicate low blood glucose but may also be seen with other conditions.
An insulin test may also be done if you have had or are suspected of having insulin resistance. This may include people with type 2 diabetes, polycystic ovary syndrome (PCOS), prediabetes, acanthosis nigricans (an abnormal skin condition), heart disease, or metabolic syndrome.
A health care practitioner also may order insulin and C-peptide tests after an insulinoma has been successfully removed to verify the effectiveness of treatment and order the tests periodically to monitor for recurrence.
Periodic testing may also be used to monitor the success of an islet cell transplant by measuring the insulin-producing capacity of the transplant.
Finding an Insulin Test
How can I get an insulin test?
An insulin test is typically ordered by your doctor if your glucose levels are off or if you complain about certain symptoms. You may also be able to visit a lab or order an insulin test online.
Can I take the test at home?
No. Although glucose levels can be monitored at home, insulin tests require specialized instruments and training and are performed at laboratories.
How much does the test cost?
The cost of insulin tests, like other blood tests, will vary depending on what your health insurance covers and where you have the test taken. If you have insurance, it should partially or fully cover the cost, but you might be responsible for a copayment or paying toward a deductible.
Insulin tests cost around $60 if paid out of pocket.
Taking an Insulin Test
An insulin test is a blood test taken from a vein in your arm.
Before the test
Because insulin levels spike and drop when you eat and drink, for this test, you will usually have to fast for 10 to 12 hours. Usually, you will get tested early in the morning. In addition, if you are taking high-dose biotin supplements (also called vitamin B7), stop using them at least 24 hours before your exam because biotin can interfere with the test.
During the test
Insulin tests involve taking a blood sample from a vein in your arm. The health practitioner drawing your blood will tie an elastic band around your upper arm to help find your vein. Then they will clean the area where they will draw the blood from. After the needle is inserted, you will feel a slight pinch. The blood sample will fill up a tube that is attached.
Once enough blood is collected, the tourniquet will be removed, the needle will be withdrawn, and you’ll be told to apply a bit of pressure on the blood draw site, which will be covered with gauze and a bandage.
After the test
There should not be any side effects or restrictions after your insulin test. You may have slight bruising on your arm.
Insulin Test Results
Receiving test results
Insulin test results typically take one to three days. Check in with your doctor, or they may call you directly. Depending on the lab or health care facility you used, you may also be able to access your results online via a patient portal or app.
Interpreting test results
Insulin levels must be evaluated in context.
|Disorder||Fasting insulin level||Fasting glucose level|
|Insulin resistance||High||Normal or somewhat elevated|
|Not enough insulin produced by the beta cells (as seen in type 1 diabetes or pancreatitis, for example)||Low||High|
|Hypoglycemia due to excess insulin (may be seen in insulinomas, Cushing’s syndrome, and excess administration of exogenous insulin)||Normal or high||Low|
Elevated insulin levels are seen with:
- Cushing’s syndrome
- Use of drugs such as corticosteroids, levodopa, oral contraceptives
- Fructose or galactose intolerance
- Insulin resistance, such as appears in type 2 diabetes, acanthosis nigricans, and metabolic syndrome
Decreased insulin levels are seen with:
- Type 1 diabetes
- Pancreatic diseases such as chronic pancreatitis (including cystic fibrosis) and pancreatic cancer
If your insulin test results indicate a possible issue, discuss the results further with your doctor. Some questions you may ask:
- How low or high was my insulin level?
- What are the possible explanations for my insulin test results?
- Should the test be repeated, or are there other tests that should be done to confirm a diagnosis?
A.D.A.M. Medical Encyclopedia. Insulinoma. Updated August 29, 2020. Accessed November 29, 2022. https://medlineplus.gov/ency/article/000387.htm
Centers for Disease Control. Insulin Resistance and Diabetes. Updated August 10, 2021. Accessed November 29, 2022. https://www.cdc.gov/diabetes/basics/insulin-resistance.html
MedlinePlus: National Library of Medicine. Diabetes Type 1. Updated June 29, 2020. Accessed November 29, 2022. https://medlineplus.gov/diabetestype1.html
MedlinePlus: National Library of Medicine. Diabetes Type 2. Updated May 28, 2021. Accessed November 29, 2022. https://medlineplus.gov/diabetestype2.html
MedlinePlus: National Library of Medicine. Hypoglycemia. Updated November 19, 2021. Accessed November 29, 2022. https://medlineplus.gov/hypoglycemia.html
MedlinePlus: National Library of Medicine. Insulin in Blood. Updated March 4, 2021. Accessed November 29, 2022. https://medlineplus.gov/lab-tests/insulin-in-blood/
National Institute of Diabetes and Digestive and Kidney Disease. Low Blood Glucose (Hypoglycemia). Updated July 2021. Accessed November 29, 2022. https://www.niddk.nih.gov/health-information/diabetes/overview/preventing-problems/low-blood-glucose-hypoglycemia