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Also known as: 5-Hydroxy Tryptamine; 5-HT
Formal name: Serotonin
Related tests: 5-HIAA; Chromogranin A

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.