5-HIAA
Overview
5-Hydroxyindoleacetic acid (5-HIAA) is the primary urinary metabolite of serotonin, formed by monoamine oxidase and aldehyde dehydrogenase metabolism in the liver, kidney, and brain. It reflects systemic serotonin production and turnover, primarily from enterochromaffin cells in the gut but pathologically elevated in serotonin-producing neuroendocrine tumors. High urinary 5-HIAA levels indicate carcinoid syndrome or other serotonin-secreting tumors, while low levels lack established clinical significance. Clinically, 5-HIAA measurement is essential for diagnosing and monitoring carcinoid tumors and neuroendocrine neoplasms.
Clinical Use Cases
- Diagnosis of carcinoid syndrome and midgut neuroendocrine tumors.
- Monitoring treatment response and tumor burden in metastatic carcinoid.
- Screening for serotonin-producing neuroendocrine neoplasms.
- Evaluation of diarrhea and flushing of unknown etiology.
- Assessment of therapeutic somatostatin analog efficacy.
Specimen Types
- 24-hour urine collection.
- Plasma (less common, research use).
Measurement Methods
- High-performance liquid chromatography (HPLC) with electrochemical or fluorescence detection.
- Liquid chromatography-tandem mass spectrometry (LC-MS/MS).
- Colorimetric assays (historical).
Test Preparation and Influencing Factors
- Strict 48-hour low-serotonin diet (avoid bananas, pineapple, walnuts, tomatoes, avocados, eggplant, kiwi).
- Avoid medications affecting serotonin metabolism (MAOIs, SSRIs, acetaminophen, cough syrups).
- Complete 24-hour urine collection with acid preservative.
- Incomplete collection or non-compliance with diet causes false results.
- Renal function affects excretion; dehydration concentrates sample.
Synonyms
- 5-Hydroxyindoleacetic acid.
- Serotonin metabolite.
- HIAA.