5-HIAA is a urine test that measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) -- a breakdown product of a hormone called serotonin.

This test tells how much 5-HIAA the body is producing.

HIAA; 5-hydroxyindole acetic acid; Serotonin metabolite

A 24-hour urine sample is needed.

• On day 1, urinate into the toilet when you get up in the morning.
• Afterwards, collect all urine in a special container for the next 24 hours.
• On day 2, urinate into the container when you get up in the morning.

Cap the container. Keep it in the refrigerator or a cool place during the collection period.

Label the container with your name, the date, the time of completion, and return it as instructed.

For an infant, thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on the infant. For males, place the entire penis in the bag and attach the adhesive to the skin. For females, place the bag over the labia. Diaper as usual over the secured bag.

This procedure may take a couple of attempts -- lively infants can move the bag, causing the urine to be absorbed by the diaper. Check the infant frequently and change the bag after the infant has urinated into it. Drain the urine from the bag into the container provided by your health care provider.

Deliver it to the laboratory or your health care provider as soon as possible upon completion.

Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.

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

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

You will be told not to eat certain foods for 3 days before the test. Foods that can interfere with 5-HIAA measurements include plums, pineapples, bananas, eggplant, tomatoes, avocados, and walnuts.

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

This test measures the level of 5-HIAA in the urine. It is often done to detect tumors in the digestive tract (carcinoid tumors) and to track a patient's condition.

The urine test may also be used to diagnose mastocytosis and endocrine tumors.

The normal range is 2 to 6 milligrams per 24 hours (mg/24 hr).

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

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

Abnormal results may be due to:

• Tumors of the endocrine system or the digestive tract
• Mastocytosis

This list is not all-inclusive.

There are no risks.

Hande KR. Carcinoid syndrome. In Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 240.