5-Hydroxyindoleacetic acid

5-HIAA is tested by 24-hour urine samples combined with an acidic additive to maintain pH below 3. Certain foods like pineapple, kiwi, banana, walnuts and drugs such as acetaminophen, nicotine or caffeine are known to interfere with the measurement. Low levels of 5-HIAA in the cerebrospinal fluid have been associated with aggressive behavior and suicide by violent means, correlating with diminished serotonin levels. Elevated serotonin (hyperserotonemia) is one of the most common biological findings in autism and 5-HIAA may be elevated in patients with autistic spectrum disorders. ==Limitations==

5-HIAA may be normal with nonmetastatic carcinoid tumor and may be normal even with the carcinoid syndrome, particularly in subjects without diarrhea, because some patients with the carcinoid syndrome excrete nonhydroxylated indolic acids. • Midgut carcinoids are most apt to produce carcinoid syndrome with 5-HIAA elevation. Patients with renal disease may have falsely low 5-HIAA levels in the urine. The production and metabolism of serotonin, and thus 5-HIAA, is dependent upon the tissue of origin of the tumor. Tumors from midgut cells, such as ileal carcinoid usually contain and release large quantities of serotonin. These amounts may not be fully reflected in the amount of 5-HIAA in urine, because little is metabolized. Foregut tumors lack the decarboxylase enzyme necessary to convert 5-hydroxytryptophan to serotonin, resulting in minimal to no elevation in urinary 5-HIAA levels. Tumors derived from hindgut cells (rectal carcinoid) rarely produce excess serotonin or 5-HIAA. Of 75 patients with carcinoid tumors, 75% had above normal urinary 5-HIAA excretion and 64% had above normal serotonin excretion. ==References==