5-hydroxyindole acetic acid

5-Hydroxyindoleacetic acid (5-HIAA) is the main metabolite of serotonin, a significant neurotransmitter. It is often measured in the urine of patients suspected of having carcinoid syndrome, a group of symptoms associated with carcinoid tumors which secrete large amounts of serotonin into the bloodstream.

Chemistry

5-HIAA is an indole compound produced through the metabolic breakdown of serotonin. The process begins with the enzymatic conversion of serotonin to 5-hydroxyindoleacetic acid by the enzyme monoamine oxidase (MAO), followed by aldehyde dehydrogenase. The resulting compound is then excreted in the urine.

Clinical significance

In a clinical setting, the measurement of 5-HIAA levels in the urine is a key diagnostic tool for detecting carcinoid tumors. These tumors, which can occur in the gastrointestinal tract, lungs, and other parts of the body, produce excessive amounts of serotonin. This overproduction leads to an increase in 5-HIAA, which can be detected in the urine.

Patients with suspected carcinoid syndrome are often instructed to avoid certain foods and medications that can affect serotonin levels and thus interfere with the test results. These include bananas, avocados, plums, eggplants, tomatoes, and certain drugs such as monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants, and cough medicines containing dextromethorphan.

See also

• Serotonin
• Carcinoid syndrome
• Indole