Definition of 5-HIAA:

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.

How the test is performed:

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.

How to prepare for the test:

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 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 particular foods for 3 days before the test. Foods that can interfere with 5-HIAA measurements include plums, pineapples, bananas, eggplant, tomatoes, avocados, and walnuts.

How the test will feel:

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

Why the test is performed:

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.