Serotonin

Overview

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter derived from tryptophan that transmits nerve impulses, constricts blood vessels, regulates mood, and influences gastrointestinal motility and sleep-wake cycles. Over 90% of circulating serotonin is stored in platelets, with the remainder produced by enterochromaffin cells in the gut and brain neurons. Elevated levels, often due to serotonin-secreting carcinoid tumors, may indicate carcinoid syndrome, characterized by flushing, diarrhea, and heart issues, while low levels are not typically assessed via blood tests. Clinically, it aids in diagnosing and evaluating neuroendocrine tumors when used alongside 5-HIAA or chromogranin A, though many tumors do not elevate it.pmc.ncbi.nlm.nih+3

Clinical Use Cases

  • Diagnosis of carcinoid syndrome, especially with symptoms like flushing, diarrhea, and rapid heart rate.pmc.ncbi.nlm.nih+1
  • Adjunct to urinary 5-HIAA and serum chromogranin A for detecting serotonin-producing neuroendocrine tumors.labcorp+1
  • Follow-up testing in patients with known or treated carcinoid tumors.[logan.testcatalog]​
  • Differential diagnosis of isolated symptoms suggestive of carcinoid tumors when first-line tests are inconclusive.[mlabs.umich]​

Specimen Types

  • Serum (from red-top or gel-barrier tube, separated within 30 minutes).[pmc.ncbi.nlm.nih]​
  • Whole blood (frozen, as most serotonin is platelet-bound).cdos.halfpenny+1
  • Platelet-rich plasma (less common).[pubmed.ncbi.nlm.nih]​

Measurement Methods

  • Liquid chromatography/tandem mass spectrometry (LC/MS-MS).labcorp+1
  • High-performance liquid chromatography (HPLC) with electrochemical detection (ECD).pubmed.ncbi.nlm.nih+1
  • Fluorescence or UV detection paired with HPLC.[pmc.ncbi.nlm.nih]​

Test Preparation and Influencing Factors

  • Avoid serotonin-rich foods (avocados, bananas, pineapples, plums, walnuts, tomatoes, etc.) for 3 days before and during collection.testing+1
  • Discontinue monoamine oxidase inhibitors (MAOIs) for at least 1 week prior.[pmc.ncbi.nlm.nih]​
  • Certain drugs like lithium, methyldopa, morphine, reserpine elevate levels; selective serotonin reuptake inhibitors (SSRIs) may reduce them.mlabs.umich+1
  • Separate serum from cells within 30 minutes; some labs recommend overnight fasting.testing+1
  • Patient’s sex should be noted on request form.[pmc.ncbi.nlm.nih]​

Synonyms

Further Reading