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SI UNITS (recommended)


* The SI units is the recommended method of reporting clinical laboratory results

5-hydroxytryptamine (5-HT), 5-OH Tryptamine, Hippophaine
Units of measurement
µmol/L, µg/L, µg/dL, µg/100mL, µg%, ng/mL

Serotonin is a biochemical messenger and regulator, synthesized from the essential amino acid L-Tryptophan. 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. In humans it is found primarily in the central nervous system, gastrointestinal tract, and blood platelets. Serotonin mediates several important physiological functions including neurotransmission, gastrointestinal motility, stimulant of smooth muscle contraction, prolactin release, and GH release; and functions in hemocoagulationhemostasis, and cardiovascular integrity.

Serotonin in the nervous system acts as a local transmitter at synapses, and as a paracrine or hormonal modulator of circuits upon diffusion, allowing a wide variety of "state-dependent" behavioral responses to different stimuli. In vertebrates, which display a wider and much more sophisticated behavioral repertoire, serotonin also modulates sleep, the arousal state , sexual behavior, and others, and deficiencies of the serotonergic system causes disorders such as depression, obsessive-compulsive disorder, phobias, posttraumatic stress disorder, epilepsy, and generalized anxiety disorder. Serotonin has three different modes of action in the nervous system: as transmitter, acting locally at synaptic boutons; upon diffusion at a distance from its release sites, producing paracrine (also called volume) effects, and by circulating in the blood stream, producing hormonal effects. The three modes can affect a single neuronal circuit.


  • 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
Reference Intervals

50–200 ng/mL.

Lab units Conversion Calculator. Convert Serotonin level to µmol/L, µg/L, µg/dL, µg/100mL, µg%, ng/mL . Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Serotonin.