What is 5-HIAA (Neurotransmitter)?

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

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