5-hydroxyindoleacetic acid

5-Hydroxyindoleacetic acid (5-HIAA) is a primary metabolite of serotonin, a key neurotransmitter in the central nervous system. It is produced via the action of the enzyme monoamine oxidase on serotonin, followed by further oxidation. 5-HIAA is excreted in the urine and is often measured to assess serotonin levels in the body.

Biological significance

5-HIAA is an important marker in the diagnosis of carcinoid syndrome, a condition caused by carcinoid tumors that secrete large amounts of serotonin. Elevated levels of 5-HIAA in the urine can indicate the presence of these tumors. Normal levels of 5-HIAA in the urine are typically between 2 to 8 mg over 24 hours.

Clinical testing

The measurement of 5-HIAA is typically performed using a 24-hour urine collection. 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.

Pathophysiology

Increased levels of 5-HIAA can be indicative of neuroendocrine tumors, particularly those originating in the gastrointestinal tract. These tumors can lead to an overproduction of serotonin, which is then metabolized to 5-HIAA. Conversely, low levels of 5-HIAA may be associated with serotonin deficiency disorders.

Also see

• Serotonin
• Carcinoid syndrome
• Neuroendocrine tumor
• Monoamine oxidase
• Urine test