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5-oxyindoleacetic acid in urine
Last reviewed: 04.07.2025
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Reference values (norm) for the concentration of 5-hydroxyindoleacetic acid in a single portion of urine in adults are less than 25 mg/day (<131 μmol/day), the content in daily urine is 2-7 mg/day (10.5-36.6 μmol/day).
5-Hydroxyindoleacetic acid (5-hydroxyindoleacetic acid) is the end product of serotonin metabolism. Determination of its concentration in urine is more useful than testing serotonin levels in blood for diagnosing carcinoid tumors. The study requires special preparation of the patient - exclusion from the diet of foods containing 5-hydroxyindoles (walnuts, bananas, avocados, eggplants, pineapples, plums, tomatoes) and some medications (corticotropin, salicylates, imipramine, levodopa, monoamine oxidase inhibitors, isoniazid, ethanol). The content of 5-hydroxyindoleacetic acid in a single portion of urine over 25 mg/day (over 131 μmol/day) is considered diagnostically significant for carcinoid syndrome. An increase in 5-hydroxyindoleacetic acid is observed in carcinoid tumors of the middle (most often the ileum) and upper ( pancreas, duodenum, bile ducts) parts of the gastrointestinal tract. In carcinoid tumors with metastases, the level of 5-hydroxyindoleacetic acid often exceeds 350 mg/day (1820 μmol/day).
Increased levels of 5-hydroxyindoleacetic acid are found in testicular carcinoid tumors, celiac disease, Whipple's disease, oat cell carcinoma of the bronchi, and carcinoid-type bronchial adenoma. Lower intestinal tumors (rectum) rarely produce 5-hydroxyindoleacetic acid.
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