Serotonin, Blood


Serotonin (5-hydroxytryptamine or 5-HT) is a neurotransmitter that has a major role in multiple states including aggression, pain, sleep, appetite, anxiety, depression, migraine and emesis (vomiting). Serotonin in the body is derived from dietary tryptophan, which is converted by a number of enzymes to 5-HT. The breakdown products of serotonin are excreted in the urine as 5-hydroxyindole acetic acid (5-HIAA). Drugs such as monoamine oxidase inhibitors, selective serotonin re-uptake inhibitors, and tricyclic antidepressants can block serotonin degradation leading to increased serotonin levels. Serotonin toxicity results from an increase in intra-synaptic 5-HT levels in the CNS. Serotonin toxicity can be thought of as a triad of clinical features consisting of: (1) autonomic signs, (2) neuromuscular changes and (3) altered mental status. See Also 5-Hydroxy-Indole Acetic Acid (5-HIAA), 24 Hrs Urine p.7 and 5-Hydroxytryptophan (5-HTP), Plasma


Markedly increased serotonin levels are associated with metastasising abdominal carcinoid tumours. Slight increases in serotonin are found in dumping syndrome, acute intestinal obstruction, cystic fibrosis, acute myocardial infarction and non-tropical sprue. In addition, benign cystic teratomas and tumours producing atypical carcinoid syndrome are associated with increased serotonin levels. Decreased levels are found in Down’s syndrome, untreated phenylketonuria, Parkinson’s disease and severe depression.

Sample Type, Quantity & Conditions

2 ml EDTA Whole Blood Frozen

Special Precautions

Normal Range

68 - 232 ng/ml

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