5-hydroxyindoleacetic acid (5-HIAA) /hīdrok′sē·in′dōlē·əset″ik/ , an acid produced by serotonin metabolism, measured in the blood and urine to aid in the diagnosis of certain kinds of tumors. It commonly rises above normal levels in whole blood in association with asthma, diarrhea, rapid heartbeat, and other symptoms and is elevated in the urine of patients with carcinoid syndrome. Its normal concentration in whole blood is 0.05 to 0.20 g/mL; its normal accumulation in urine after 24-hour collection is 1 to 5 mg.
