| 5-HIAA | <biochemistry, tumour marker> This is a metabolite of serotonin that is excreted in the urine. Serotonin is a neurotransmitter that is synthesised from the amino acid tryptophan by enterochromaffin cells in the gut and bronchi. It is metabolised to 5-hydroxyindole acetic acid in the liver and then excreted in the urine. Elevations in 5-hydroxyindole acetic acid can indicate carcinoid tumour. The normal range in a 24 hour urine collection is 3 to 15 mg per 24 hours. Acronym: 5-HIAA (13 Nov 1997) |
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