5hydroxyindole3acetic

5-hydroxyindole-3-acetic acid, commonly abbreviated 5-HIAA, is a major metabolite of serotonin (5-hydroxytryptamine) in humans. It is formed when serotonin is oxidatively deaminated by monoamine oxidase to 5-hydroxyindoleacetaldehyde, which is subsequently oxidized to 5-HIAA by aldehyde dehydrogenase. The molecule is excreted primarily in urine, and its levels in 24-hour urine samples or plasma reflect overall serotonin turnover in the body.

In clinical practice, 5-HIAA is used as a biomarker for serotonin-secreting tumors, notably carcinoid tumors. Elevated urinary or plasma 5-HIAA can support the diagnosis of carcinoid syndrome and is sometimes used to monitor disease or response to treatment. However, several factors can influence results, including diet and medications. Diets rich in serotonin-containing foods, such as certain fruits (bananas, avocados, kiwifruit, tomatoes, pineapples) and other sources, can increase 5-HIAA levels and cause false positives. Certain drugs and supplements may also affect results, so testing is typically accompanied by pre-analytic instructions to reduce confounding factors.

Analytical methods for measuring 5-HIAA include high-performance liquid chromatography (HPLC) with electrochemical or fluorometric detection and liquid chromatography–mass spectrometry (LC-MS). These methods provide specificity and sensitivity suitable for clinical diagnostics. 5-HIAA is also considered in research on serotonin metabolism, neuroendocrine function, and related disorders.