5-HIAA

5-Hydroxy-indole-acetic acid (5-HIAA) is the metabolite of 5-hydroxytryptamine (serotonin). Serotonin is produced by the argentaffin cells of the GI tract. Serotonin is over-produced in the carcinoid tumours of the GI tract. These are associated with flushing attacks, diarrhoea and abdominal pain. Most carcinoid tumours are metastatic to the liver at the time of detection. Resection of the primary tumour, partial hepatectomy and embolization are the primary forms of treatment, although radiolabelled octreotide has been used more recently. 5-HIAA is invariably increased in classical carcinoid, although some tumours may be non-secretory. 5-HIAA is also increased with high dietary serotonin intake or other GI tract disease e.g. coeliac disease.