5-Hydroxy- 3-Indole Acetic Acid (5-HIAA)

The 5-Hydroxy-3-Indole Acetic Acid (5-HIAA), Urine test measures the amount of 5-HIAA, the primary breakdown product of serotonin, in a 24-hour urine sample. Serotonin is a naturally occurring chemical involved in several body functions, including digestion, mood, and blood vessel regulation. Measuring its metabolite, 5-HIAA, helps evaluate conditions associated with increased serotonin production, particularly certain neuroendocrine (carcinoid) tumors. This test provides valuable information when used alongside clinical findings and other diagnostic investigations.

Who should get this test done?

This test is recommended for:

●     Individuals experiencing unexplained flushing, diarrhea, or abdominal discomfort
●     Individuals suspected of having a carcinoid tumor or neuroendocrine tumor
●     Individuals already diagnosed with a carcinoid tumor who need treatment monitored
●     Individuals with incidental findings on imaging suggestive of a neuroendocrine growth
●     Individuals with symptoms pointing toward carcinoid syndrome, like rapid heartbeat or wheezing
Why consider this test?

This is genuinely the go-to test when carcinoid syndrome is on the table, since it picks up on elevated serotonin breakdown with strong accuracy. Carcinoid tumors tend to grow slowly and often don’t cause obvious problems early on, so catching the syndrome through this test can lead to diagnosis well before symptoms become severe. For patients already being treated, repeat testing over time gives doctors a way to track whether treatment is actually bringing serotonin levels back down, rather than guessing based on symptoms alone, which can fluctuate for other reasons too.

More information

This panel includes three components: the 5-HIAA concentration itself, the total urine volume collected, and the 24-hour 5-HIAA output calculated from both. Getting a reliable result depends heavily on following collection instructions properly, and most labs ask patients to avoid certain foods like bananas, tomatoes, and walnuts beforehand, since these can artificially raise 5-HIAA levels and throw off the reading.

Other names of the test

●     5-HIAA urine test
●     Hydroxyindoleacetic acid test
●     Serotonin metabolite test
●     Carcinoid syndrome urine test
●     24-hour urine serotonin metabolite test