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Serotonin Blood Test

Last updated July 9, 2019

Approved by: Maulik P. Purohit MD MPH

Serotonin Blood Test is a test that measures serotonin in your blood.


What are the other Names for this Test? (Equivalent Terms)

  • 5-HT Blood Test
  • 5-Hydroxy Tryptamine Blood Test

What is Serotonin Blood Test? (Background Information)

  • Serotonin: The chemical serotonin, produced in the brain, is a neurotransmitter derived from the amino acid tryptophan. Certain cells, along the digestive and respiratory tract, are the areas of storage for 90% of the body’s serotonin
  • The serotonin balance is found in the brain cells (neurons) of the central nervous system. Research has shown that serotonin plays an important role with memory and learning, sleep and mood regulation, depression, etc. Intestinal movements are also controlled by serotonin. It is also present in the blood platelets and help in constriction of blood vessels, which is vital in preventing blood loss, when the blood vessels are injured
  • The level of serotonin in the body is important. It has to be maintained and regulated in an optimal manner. Studies have shown that any disruption in serotonin levels leads to many adverse complications
  • The liver has strong enzymes to neutralize most excess hormones produced, by breaking them down into metabolites (products of metabolism). This breakdown process controls the level of serotonin in blood and prevents it from reaching high levels in body. One of the most important metabolite (a breakdown product) produced is 5-hydroxyindoleacetic acid (5-HIAA)
  • Carcinoid tumors: These tumors are characterized by their secretion of large amounts of the hormone serotonin and hence, they are considered a type of endocrine tumors. They occur mostly (65%) in the gastrointestinal tract and in the lungs and airways (25%). The amino acid tryptophan is converted by these tumors to serotonin in significant quantities. When this overproduced serotonin reaches the tissues in the lungs or gastrointestinal region, they produce a set of debilitating symptoms, known as carcinoid syndrome (CS)

What are the Clinical Indications for performing the Serotonin Blood Test?

In the early stages, carcinoid tumors are extremely difficult to diagnose due the lack of any significant symptoms.  Many a times they are discovered accidentally, or only after the carcinoid syndromemanifest. A Serotonin Blood Test is performed in individuals with the following set of non-specific symptoms that point to carcinoid tumors. These include:

  • Flushing (sudden reddening around the face and neck region) with no sweating , increased heart beat rate/palpitations
  • Heart diseases due to heart valve problems
  • Nocturnal diarrhea, vomiting, and nausea
  • Difficulty in breathing, cough
  • Abdominal pain

Additionally, those undergoing treatment for carcinoid tumor have to be regularly tested and monitored. In these individuals, serotonin levels are performed to determine the whether treatment is working well, or if the tumor has recurred.

How is the Specimen Collected for Serotonin Blood Test?

Sample required: Blood

Process: Insertion of needle into a vein (arm).

Preparation required: None

What is the Significance of the Serotonin Blood Test Result?

  • Abnormally elevated levels of serotonin in blood samples combined with the carcinoid syndrome symptoms may indicate the presence of a carcinoid tumor. However, in order to confirm the biochemical test results and/or detect location of the tumor, imaging scans are performed. This may be followed by a biopsy of the affected tumor
  • If the above described symptoms are manifest, but serotonin or 5-HIAA tests indicate normal levels; then, further study analysis is required to diagnose carcinoid tumors. The normal levels may occur, because not all carcinoid tumors secrete the serotonin hormone
  • For those already detected with carcinoid tumors producing serotonin, regular testing for serotonin levels, help evaluate the treatment effectiveness

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

Certain medications (morphine, reserpine, lithium, etc.), alcohol, smoking, caffeine, imbalances caused by other hormones, and many other factors are known to influence body serotonin levels.

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 7, 2013
Last updated: July 9, 2019