5-HIAA

5-Hydroxyindoleacetic acid (5-HIAA) is a primary metabolite of serotonin, a crucial neurotransmitter in the central nervous system. It is produced through the breakdown of serotonin by the enzyme monoamine oxidase and is subsequently excreted in the urine. The measurement of 5-HIAA levels in urine is often used as a diagnostic tool for various medical conditions, particularly those related to serotonin metabolism.

Biochemistry

5-HIAA is formed when serotonin is metabolized by the enzyme monoamine oxidase to form 5-hydroxyindoleacetaldehyde, which is then further oxidized to 5-HIAA by the enzyme aldehyde dehydrogenase. This process primarily occurs in the liver and the gastrointestinal tract.

Clinical Significance

The measurement of 5-HIAA in urine is particularly useful in the diagnosis of carcinoid syndrome, a condition caused by carcinoid tumors that secrete large amounts of serotonin. Elevated levels of 5-HIAA can indicate the presence of these tumors. Normal levels of 5-HIAA in urine are typically less than 10 mg per 24 hours, but this can vary depending on dietary intake and other factors.

Testing and Diagnosis

To measure 5-HIAA levels, a 24-hour urine sample is usually collected. Patients are often advised to avoid certain foods and medications that can interfere with the test, such as bananas, avocados, and certain cough medicines, as these can artificially elevate 5-HIAA levels.

Related Conditions

• Carcinoid syndrome
• Serotonin syndrome
• Neuroendocrine tumors

See Also

• Serotonin
• Monoamine oxidase
• Neurotransmitter
• Carcinoid tumor
• Urine test