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Also known as: HIAA; Serotonin metabolite
Formal name: 5-hydroxyindoleacetic acid
Related tests: Serotonin; Chromogranin A

At a Glance

Why Get Tested?

To help diagnose and monitor treatment for a serotonin-secreting carcinoid tumor

When to Get Tested?

When you have symptoms suggestive of a carcinoid tumor such as flushing, diarrhea, and/or wheezing, and at intervals following treatment

Sample Required?

Test Preparation Needed?

You may be instructed to avoid certain foods and medications prior to this test.

The Test Sample

What is being tested?

This test measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) in the urine. 5-HIAA is the primary metabolite of serotonin, a chemical derived from the amino acid tryptophan. Serotonin is produced as needed by the nervous system, mainly the brain, but also special cells in the bronchial tubes (lungs) and gastrointestinal (GI) tract. It helps transmit nerve impulses and constrict blood vessels, participates in the wake-sleep cycle, and affects mood. After it is used by the body, serotonin is broken down in the liver, and its metabolites, including 5-HIAA, are excreted in the urine.

Ordinarily, only small varying amounts of 5-HIAA are present in the urine. Large quantities of serotonin and 5-HIAA may be produced, however, by some carcinoid tumors. Carcinoid tumors are slow-growing noncancerous or cancerous neuroendocrine masses that can form in the GI tract, on the appendix, and in the lungs. About 2 out of every 3 carcinoids are found in the GI tract with most of the rest occurring in the lungs, though they may affect other organs as well. According to the American Cancer Society, there are about 11,000 to 12,000 neuroendocrine tumors or cancers diagnosed each year in United States. Many more of these tumors may exist, but most remain small and do not cause any symptoms. When carcinoid tumors are discovered in asymptomatic patients during surgical procedures performed for other reasons, they are called "incidental" tumors. A small percentage of these tumors may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.

About 10% of carcinoid tumors, primarily those found in the GI tract with liver involvement, will produce enough serotonin to cause symptoms, such as flushing of the face, diarrhea, a rapid heart rate, and wheezing, which are referred to as carcinoid syndrome. The serotonin that causes carcinoid syndrome may be released continuously or intermittently and can lead to significantly increased quantities of 5-HIAA in the urine.

How is the sample collected for testing?

For the 24-hour urine collection, all of the urine should be saved for a 24-hour period. It is best to keep the sample in a cool, dark place, such as a refrigerator.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

Pre-sample preparation is important for accurate 5-HIAA test results. Foods such as avocados, bananas, pineapples, plums, walnuts, tomatoes, kiwi fruit, and eggplant can interfere with 5-HIAA measurement and should be avoided for 3 days prior to and during urine collection. There are also a variety of drugs that can affect the 5-HIAA test, but you should talk to your doctor before decreasing or discontinuing any medications.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 555-556.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 584-587.

Dugdale, D. (2008 November 10). 5-HIAA. MedLinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003612.htm. Accessed July 2010.

(Revised 2009 June 06). Detailed Guide: Gastrointestinal Carcinoid Tumors. American Cancer Society [On-line information]. Available online at http://www.cancer.org/docroot/CRI/CRI_2_3x.asp?rnav=cridg&dt=14 through http://www.cancer.org. Accessed July 2010.

(Revised 2010 March 18). Detailed Guide: Lung Carcinoid Tumor. American Cancer Society [On-line information]. Available online at http://www.cancer.org/docroot/CRI/CRI_2_3x.asp?rnav=cridg&dt=56 through http://www.cancer.org. Accessed July 2010.

(2010 February). Carcinoid Tumor. Cancer.Net, American Society of Clinical Oncology [On-line information]. Available online at http://www.cancer.net/patient/Cancer+Types/Carcinoid+Tumor through http://www.cancer.net. Accessed July 2010.

(Modified 2008 May 16) Gastrointestinal Carcinoid Tumors Treatment (PDQ®), Health Professional Version [On-line information]. Available online at http://www.cancer.gov/cancertopics/pdq/treatment/gastrointestinalcarcinoid/HealthProfessional through http://www.cancer.gov. Accessed July 2010.

Santacroce, L. and Diomede, L. (Updated 2009 November 19). Malignant Carcinoid Syndrome. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/282515-overview through http://emedicine.medscape.com. Accessed July 2010.

Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds (2005). Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 2224-2225.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 497-498.

(2005). Gastrointestinal Carcinoid Tumors, A Detailed Guide. American Cancer Society [On-line information]. Available online at http://www.cancer.org/docroot/CRI/CRI_2_3x.asp?dt=14 through http://www.cancer.org.

Nanda, R. (2005 April 15, Updated). 5-HIAA. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003612.htm.

Brose, M. (2004 August 3, Updated). Carcinoid Syndrome. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000347.htm.

Zuetenhorst, J. et. al. (2004 July 9). Daily Cyclic Changes in the Urinary Excretion of 5-Hydroxyindoleacetic Acid in Patients with Carcinoid Tumors. Clinical Chemistry [On-line journal]. Available online at http://www.clinchem.org/cgi/content/full/50/9/1634 through http://www.clinchem.org.

(© 2006). 5-Hydroxyindoleacetic Acid (HIAA), Urine. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_a349.jsp#1152320 through http://www.aruplab.com.

Datta, V. (2005 May 17, Updated). Serum serotonin level. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm.

Sweeney, J. and Rosemurgy, A. (1997 January/February). Carcinoid Tumors of the Gut. Cancer Control Journal v4 (1) [On-line journal]. Available online at https://www.moffitt.usf.edu/pubs/ccj/v4n1/article2.htm through https://www.moffitt.usf.edu.

Strosberg, J. et. al. (2006 January). Selective Hepatic Artery Embolization for Treatment of Patients With Metastatic Carcinoid and Pancreatic Endocrine Tumors. Cancer Control Journal v13 (1) [On-line journal]. Available online at https://www.moffitt.usf.edu/pubs/ccj/ through https://www.moffitt.usf.edu.

Johnson, R. et. al. (2003 November). Ethanol Origin in Postmortem Urine: A LC/MS Determination of Serotonin Metabolites. Federal Aviation Administration [On-line Medicine Technical Report]. Available online through http://www.faa.gov