5 HIAA – 5 Hydroxy Indole Acetic Acid

This test finds out how much 5-hydroxyindoleacetic acid (5-HIAA) is in your urine. This acid is a waste product that comes from the breakdown of serotonin by the liver. Serotonin is a hormone that plays a role in transmitting nerve impulses. It also affects your sleep and mood. Your body normally gets rid of 5-HIAA in your urine.

You may have higher levels of 5-HIAA in your urine if you have a carcinoid tumor. These tumors secrete serotonin.  With more serotonin in your body, more is broken down. This leads to more 5-HIAA in your urine. Because serotonin in the blood is broken down very quickly, the amount of 5-HIAA collected in the urine over a full day more accurately reflects the rate at which serotonin is being made than the blood level at one particular time.