5-HIAA is a test that measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) -- a break-down product of the chemical messenger serotonin -- in urine. This test tells how much 5-HIAA the body is removing.

The health care provider may tell you to stop taking drugs that can interfere with the test. A 24-hour urine sample is needed:

• On day 1, urinate into the toilet when you wake up in the morning.
• Collect all of your urine in a special container for the next 24 hours.
• On day 2, urinate into the container in the morning when you wake up.
• Cap the container. Keep it in the refrigerator or a cool place during the collection period. Label the container with your name, the date, and the time you complete the sample, and return it as instructed.

For an infant, thoroughly wash the area around the penis (boys) or vagina (girls). Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For boys, you can place the entire penis in the bag and attach the adhesive to the skin. For girls, place the bag over the inner and outer lips of the vagina (labia). Place a diaper over the infant (including over the bag). Check the infant often and change the bag after the infant has urinated into the bag. For active infants, this procedure may take a couple of attempts -- lively infants can displace the bag, making it hard to get the sample. Drain the urine into the container to take it to the laboratory.

Deliver the urine sample to the laboratory or your health care provider as soon as possible after you collect it. The lab analyzes the sample for the amount of 5-HIAA.

The health care provider may tell you to stop taking drugs that can interfere with the test. Do not eat foods that contain substances that interact with the test for 3 days before the test (see Special Considerations).

The test involves only normal urination, and there is no discomfort.

This test is done to check the amount of 5-HIAA the body is removing.

Serotonin is made from the amino acid tryptophan by hormone-producing enterochromaffin cells in the gut and airways of the lung (bronchi). Serotonin opens up (dilates) blood vessels and causes clumping of platelets (platelet aggregation). It is broken down in the liver to 5-HIAA and later ends up in the urine.

The normal range is 3 to 15 mg/24 hr (milligrams per 24 hours).

Health care providers usually measure 5-HIAA levels to detect tumors in the digestive tract (carcinoid tumors) and to track a patient's condition. This test is also performed to diagnose certain medical conditions, such as systemic mastocytosis and endocrine tumors.

There are no risks.

Drugs that can increase 5-HIAA measurements include acetanilid, phenacetin, glyceryl guaiacolate (found in many cough syrups), methocarbamol, and reserpine.

Drugs that can decrease 5-HIAA measurements include chlorpromazine, heparin, imipramine, isoniazid, levodopa, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, promethazine, and tricyclic antidepressants.

Foods that can interfere with 5-HIAA measurements include plums, pineapples, bananas, eggplant, tomatoes, avocados, and walnuts. Do not eat these foods for 3 days before the test.

Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, Management. 8th ed. Philadelphia, Pa: Saunders; 2006.

Goldman Lee, Ausiello D. Cecil Textbook of Medicine. 22nd ed. Philadelphia, Pa: Saunders; 2003.