5-HIAA is a serotonin metabolite.
5-HIAA is the primary metabolite of serotonin, a chemical substance (neurotransmitter) that transmits messages between nerve cells. After it is used by the body, serotonin is broken down in the liver, and its metabolites, including 5-HIAA, are excreted in the urine.
Ordinarily, only small varying amounts of 5-HIAA are present in the urine. Large quantities of serotonin and 5-HIAA may be produced, however, by some carcinoid tumors. Carcinoid tumors are slow-growing noncancerous or cancerous neuroendocrine masses that can form in the GI tract, especially in the appendix, and in the lungs.
5-Hydroxyindoleacetic acid (5-HIAA) results are expressed as a ratio to creatinine excretion (mg/g CRT).
Reference ranges (in µg/g Cr):
Ages 15 & Older:
2205 – 11816 (Optimum: 2988 – 5850)
Ages 10 – 14:
3802 – 9879
Ages < 10:
6331 – 18834