Clinical Significance
5-HIAA is tested by 24-hour urine samples combined with an acidic additive to maintain pH below 3. Certain foods and drugs are known to interfere with the measurement. 5-HIAA levels can vary depending on other complications, including tumors, renal malfunction, and small bowel resection.
Since 5-HIAA is a metabolite of serotonin, testing is most frequently performed for the diagnosis of carcinoid tumors of the enterochromaffin (Kultschitzsky) cells of the small intestine, which release large amounts of serotonin. Values greater than 25 mg per 24 hours (higher if the patient has malabsorption) are strong evidence for carcinoid.
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.
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