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.