Interpretive Handbook

Test 9248 :
5-Hydroxyindoleacetic Acid (5-HIAA), 24 Hour, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

5-Hydroxyindoleacetic acid (5-HIAA) is the major metabolite of serotonin and is excreted in the urine. Intestinal carcinoid tumors along with neuroendocrine tumors can produce excess amounts of 5-HIAA and serotonin especially in individuals with carcinoid syndrome. Carcinoid syndrome is characterized by carcinoid tumors, flushing, heart disease, and hepatomegaly.


Measurement of 5-HIAA in a 24-hour urine specimen can diagnose carcinoid disease with a high specificity.

Useful For Suggests clinical disorders or settings where the test may be helpful

Biochemical diagnosis and monitoring of intestinal carcinoid syndrome

Interpretation Provides information to assist in interpretation of the test results

Elevated excretion of 5-hydroxyindoleacetic acid is a probable indicator of the presence of a serotonin-producing tumor, if pharmacological and dietary artifacts have been ruled out.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Intake of food with a high content of serotonin (avocados, dates, eggplant, all fruit [including bananas, cantaloupe, grapefruit, kiwifruit, melons, pineapple, plantains, plums], all nuts [including hickory nuts, butternuts, pecans, walnuts], and tomatoes and tomato products) within 48 hours of the urine collection could result in falsely elevated 5-hydroxyindoleacetic acid (5-HIAA) excretion.


Numerous drugs affect the excretion of 5-HIAA by different mechanisms, including increased serotonin synthesis, metabolism, and release and inhibition of uptake. Patients should avoid taking the following medications for 48 hours before and during collection as they can falsely raise or lower 5-HIAA levels and interfere with results.

-Pain relievers (specifically those containing acetaminophen [Tylenol], salicylates [aspirin] or phenacetin)

-Cough syrups containing guaifenesin or antihistamines

-Nasal drops and sprays

-Muscle relaxants containing mephenesin or methocarbamol (Robaxin, Flexeril, and Valium for example)

-Antidepressants including tricyclic antidepressants (imipramine, for example) and monamine oxidase inhibitors (MAOIs) (Nardil, for example)

-Hypertensive medications (Reserpine, for example)

-Isoniazid (antibiotic used to fight tuberculosis and other diseases)

-Methenamine (antibiotic used to fight urinary tract infections)

-Heparin (anticoagulant used as a blood thinner)

-L-dopa (Levodopa such as Sinemet, or Methyldopa, used to treat high blood pressure, for example)

-Phenothiazines (Compazine or Thorazine for example, used to treat mental or emotional disorders)


Patient should also avoid tobacco, tea and coffee for 48 hours before and during specimen collection.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

< or =8 mg/24 hours

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. de Herder W: Biochemistry of neuroendocrine tumours. Best Pract Res Clin Endocrinol Metab 2007 Mar;21(1):33-41

2. Manini P, Andreoli R, Cavazzini S, et al: Liquid chromatography-electrospray tandem mass spectrometry of acidic monoamine metabolites. J Chromatogr B Biomed Sci Appl 2000 July 21;744(2):423-431

3. Mashige F, Matsushima Y, Kanazawa H, et al: Acidic catecholamine metabolites and 5-hydroxyindoleacetic acid in urine: the influence of diet. Ann Clin Biochem 1996;33:43-49

4. Mills K: Serotonin syndrome - A clinical update. Crit Care Clin 1997;13:763-783

5. Serotonin syndrome. In POISINDEX System. Edited by RK Klasco, CR Gelman, LT Hill. Greenwood Village, Colorado, Micromedex, 2002