Serotonin, Blood


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Subject: Serotonin, Blood

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  • Serotonin is an indole amine synthesized by the cells of the intestinal mucosa. It is stored in and transported by platelets but also found in many body tissues, including the CNS. Serotonin acts as a vasoconstrictor and neurotransmitter; stimulant of smooth muscle contraction, prolactin release, and GH release; and functions in hemocoagulation. Other names: 5-hydroxytryptamine.

  • Normal range: 50–200 ng/mL.


  • Confirming the diagnosis of carcinoid tumors.

  • Adjunct test for 5-HIAA and chromogranin-A test to follow-up patients with carcinoid tumors.


Increased In

  • Metastasizing abdominal carcinoid tumors

  • Dumpling syndrome

  • Acute intestinal obstruction

  • Cystic fibrosis

  • AMI and nontropical sprue

  • Oat cell carcinoma of the lung

  • Pancreatic islet tumor

  • Thyroid medullary carcinoma

Decreased In

  • Down syndrome

  • Severe depression

  • Parkinson disease

  • Phenylketonuria (treated and untreated)

  • Renal insufficiency

  • Teratomas


  • Blood serotonin is very unstable.

  • Medications that may affect serotonin concentrations include lithium, MAO inhibitors, methyldopa, morphine, and reserpine.

  • In general, foods that contain serotonin do not interfere significantly.

  • Slight increases may be seen in acute intestinal obstruction, acute MI, cystic fibrosis, dumping syndromes, and nontropical sprue.