At a Glance
Why Get Tested?
To help diagnose 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
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
This test measures the amount of serotonin in the blood. Serotonin is a chemical derived from the amino acid tryptophan. It is produced as needed by the nervous system, mainly the brain, but also by special cells in the bronchial tubes (lungs) and gastrointestinal tract. More than 90% of serotonin in the blood is found in the platelets. Serotonin helps transmit nerve impulses and constrict blood vessels, is a participant in the wake-sleep cycle, and affects mood. Serotonin is metabolized by the liver and its metabolites, primarily 5-HIAA (5-hydroxyindoleacetic acid, a muscle stimulant), are excreted in the urine.
Normally, serotonin is present in small varying quantities in the blood. Large quantities of serotonin and 5-HIAA may be produced continuously or intermittently by some carcinoid tumors. Carcinoid tumors are slow-growing masses that can form in the gastrointestinal tract, especially in the appendix, and in the lungs, although they may affect other organs as well. They are one of several types of tumors that arise from cells in the neuroendocrine system - cells that are found in organs throughout the body and that have both nerve and endocrine aspects. The serotonin produced by carcinoid tumors may cause symptoms such as flushing of the face, diarrhea, a rapid heart rate, and wheezing, especially when the tumor has spread to the liver. This group of symptoms is referred to as the carcinoid syndrome.
According to the American Cancer Society, there are about 11,000 to 12,000 neuroendocrine tumors or cancers diagnosed each year in the 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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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?
No test preparation is needed.
Ask a Laboratory Scientist
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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
Santacroce, L. and Balducci, L. (2010 September 1) Malignant Carcinoid Syndrome. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/282515-overview through http://emedicine.medscape.com. Accessed December 2010.
(© 1995-2010). Unit Code 84395: Serotonin, Serum. Mayo Clinic, Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/84395 through http://www.mayomedicallaboratories.com. Accessed December 2010.
Frank, E. (Updated 2010 January). Carcinoid Tumors. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CarcinoidTumors.html?client_ID=LTD through http://www.arupconsult.com. Accessed December 2010.
(Revised 2010 July 13). Detailed Guide, Gastrointestinal Carcinoid Tumors. American Cancer Society [On-line information]. Available online at http://www.cancer.org/Cancer/GastrointestinalCarcinoidTumor/DetailedGuide/index through http://www.cancer.org. Accessed December 2010.
(Revised 2010 August 17). Detailed Guide, Lung Carcinoid Tumors. American Cancer Society [On-line information]. Available online at http://www.cancer.org/Cancer/LungCarcinoidTumor/DetailedGuide/lung-carcinoid-tumor-what-is-lung-carcinoid-tumor through http://www.cancer.org. Accessed December 2010.
Vorvick, L. (Updated 2009 March 14). Serum serotonin level. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm. Accessed December 2010.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 871-873.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pg 284.
Sources Used in Previous Reviews
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 982-983.
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition]. Pp 1745.
Van Voorhees, B. W. (2007 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. Accessed on 11/1/07.
Nanda, R. (2006 September 11, Updated). Carcinoid syndrome. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000347.htm. Accessed on 11/1/07.
(2007 September, Reviewed). Carcinoid Tumors. ARUP Consult [On-line information]. Available online through http://www.arupconsult.com. Accessed on 11/1/07.
(© 2007). Serotonin, Whole Blood. ARUP's Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0080395.jsp through http://www.aruplab.com. Accessed on 11/1/07.
(© 2007). Serotonin, Serum. ARUP's Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0080397.jsp through http://www.aruplab.com. Accessed on 11/1/07.
(2006 May 1, Updated). Tryptophan. MedlinePlus Medical Encyclopedia [On-line information]. Previously available online at http://www.nlm.nih.gov/medlineplus/print/ency/article/002332.htm. Accessed on 11/1/07.