Urine Collection for 24 Hours)

The 24-Hour Urine 5-HIAA test measures the amount of 5-Hydroxyindoleacetic Acid (5-HIAA), which is the main breakdown product of serotonin, a chemical involved in mood regulation, digestion, and several other body functions.

This test is primarily used to help diagnose and monitor carcinoid tumors—rare, slow-growing tumors that often originate in the gastrointestinal tract and can secrete excessive amounts of serotonin. Measuring 5-HIAA in urine over a full 24-hour period provides a more accurate representation of serotonin metabolism than a single blood sample.