An insulin test is a blood test that measures the amount of insulin, a hormone that regulates blood sugar.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The preparation depends on the reason for testing your insulin levels. Ask your health care provider if you should fast before the test. The health care provider may ask you to stop taking medications that can interfere with the test, including injected insulin and/or oral antidiabetic medications.

For infants and children, the preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following topics:

• Infant test or procedure preparation (birth - 1 year)
• Toddler test or procedure preparation (1 - 3 years)
• Preschooler test or procedure preparation (3 - 6 years)
• School age test or procedure preparation (6 - 12 years)
• Adolescent test or procedure preparation (12 - 18 years)

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Insulin is a hormone released from the pancreas. Insulin's most important function is to help the cells take up sugar (glucose). Insulin also stimulates the production and storage of triglycerides and proteins.

Insulin is the most important regulator of blood glucose. High blood glucose (such as shortly after a meal) stimulates the release of insulin, whereas low blood glucose levels prevent insulin release.

The most important reason for measuring the blood insulin level is to diagnose or evaluate low blood sugar (hypoglycemia).

Also, insulin levels measured when someone hasn't eaten can give information about the body's sensitivity to insulin. High insulin, even with normal blood sugar, may indicate that the pancreas is working harder than normal to lower the blood-sugar level. This situation is usually caused by the body being resistant to insulin's effect -- a condition called "insulin resistance syndrome." It is very common with obesity, and hormonal problems such as polycystic ovary syndrome.

The insulin test may also be combined with other tests, such as:

• Anti-insulin antibodies
• Glucose
• Insulin C-peptide
• Proinsulin

Normal values are are 5-20 mcU/mL while fasting. (Note: mcU/mL = micro unit per milliliter)

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Greater than normal levels may indicate:

• Injection of too much insulin
• Insulinoma
• Type 2 diabetes mellitus
• Obesity
• Sulfonylurea-induced hypoglycemia

Lower than normal levels may indicate:

• Diabetes, type 1 or 2

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Obesity decreases the sensitivity of tissues to insulin. As a result, the pancreas overcompensates and makes more insulin.