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5-Hydroxy Tryptamine
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Este artigo foi modificado pela última vez em 10 de Julho de 2017.
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
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
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. In the blood, more than 90% of serotonin 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. 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.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

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

No test preparation is needed.
Accordion Title
Common Questions
  • How is it used?
    Serotonin may be ordered along with, or following, a 24-hour urine 5-HIAA test to help diagnose carcinoid tumors. It is not generally used as a monitoring tool to evaluate the effectiveness of treatment or to detect recurrence of a carcinoid tumor. Monitoring tests may include 5-HIAA and Chromogranin A.
  • When is it ordered?
    This test is primarily ordered when a patient has symptoms suggestive of a carcinoid tumor. It may be ordered initially or as a follow-up test when 5-HIAA test results are normal or near normal.
  • What does the test result mean?
    A significantly increased level of serotonin in a patient with carcinoid syndrome symptoms is suggestive but not diagnostic of a carcinoid tumor. In order to diagnose the condition, the tumor itself must be located and biopsied. The doctor will frequently follow an abnormal test result with an order for an imaging scan to help locate any tumor(s) that may be present.

    A patient with symptoms may still have a carcinoid tumor even if the concentrations of serotonin and 5-HIAA are normal. The patient may have a tumor that does not secrete serotonin or one that secretes it intermittently. A patient with no symptoms and normal or low levels of serotonin and 5-HIAA is unlikely to have a serotonin-secreting carcinoid tumor.

  • Is there anything else I should know?
    There are a variety of drugs that can affect the serotonin test, including morphine, monoamine oxidase (MAO) inhibitors such as reserpine, methyldopa, and lithium. Patients should talk to their doctor before decreasing or discontinuing any medications.

    Serotonin concentrations may be slightly increased in patients with intestinal obstructions, acute myocardial infarction (heart attack), cystic fibrosis, and dumping syndrome. The serotonin test is not usually ordered with these conditions.

  • Can I choose between the serotonin and 5-HIAA tests?
    It is up to you and your doctor to determine the tests that should be ordered. Serotonin and 5-HIAA offer complementary information. In some cases, 5-HIAA is preferred because it is more stable and, since it is collected for 24 hours, there is more chance of identifying it than excess serotonin that is only released intermittently.
  • Are some people at a higher risk for developing a carcinoid tumor?
    Anyone at any age can develop a carcinoid tumor but, according to the American Cancer Society, the average age at diagnosis is usually about 55 to 65. Patients with a family history of multiple endocrine neoplasia (MEN1), a genetic condition that increases a patient's risk of developing tumors in the endocrine system glands, may be at higher risk for developing a carcinoid tumor.
View Sources
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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 [11 paragraphs]. MedlinePlus Medical Encyclopedia [On-line information]. Accessed on: 11/1/07. Available FTP: http://www.nlm.nih.gov/medlineplus/ency/article/003562.htm

Nanda, R. (2006 September 11, Updated). Carcinoid syndrome [26 paragraphs]. MedlinePlus Medical Encyclopedia [On-line information]. Accessed on: 11/1/07. Available FTP: http://www.nlm.nih.gov/medlineplus/ency/article/000347.htm

(2007 September, Reviewed). Carcinoid Tumors [15 paragraphs]. ARUP Consult [On-line information]. Accessed on: 11/1/07. Available online

(© 2007). Serotonin, Whole Blood [6 paragraphs]. ARUP’s Laboratory Test Directory [On-line information]. Accessed on: 11/1/07. Available FTP: http://www.aruplab.com/guides/ug/tests/0080395.jsp

(© 2007). Serotonin, Serum [6 paragraphs]. ARUP’s Laboratory Test Directory [On-line information]. Accessed on: 11/1/07. Available FTP: http://www.aruplab.com/guides/ug/tests/0080397.jsp

(2006 May 1, Updated). Tryptophan [4 paragraphs]. MedlinePlus Medical Encyclopedia [On-line information]. Accessed on: 11/1/07. Available FTP: http://www.nlm.nih.gov/medlineplus/print/ency/article/002332.htm