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

      This test tells how much 5-HIAA the body is producing. It is also a way to measure how much serotonin is in the body.

  • Alternative Names
    • HIAA; 5-hydroxyindole acetic acid; Serotonin metabolite

  • 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, and 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 provider as soon as possible upon completion.

  • How to Prepare for the Test
    • Your provider will instruct you, if necessary, to stop taking medicines that may interfere with the test.

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

      Medicines 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.

  • 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 certain tumors in the digestive tract (carcinoid tumors) and to track a person's condition.

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

  • Normal Results
    • 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.

  • What Abnormal Results Mean
    • Abnormal results may be due to:

      • Tumors of the endocrine system or carcinoid tumors
      • Systemic mastocytosis

      This list is not all-inclusive.

  • Risks
    • There are no risks.

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