5-Hydroxyindoleacetic acid

A metabolite of serotonin

5-Hydroxyindoleacetic acid (5-HIAA) is a primary metabolite of serotonin, a key neurotransmitter in the central nervous system. It is commonly measured in the urine to assess serotonin levels in the body and is used in the diagnosis of various medical conditions.

Biochemistry

5-Hydroxyindoleacetic acid is produced from serotonin through the action of the enzyme monoamine oxidase (MAO), followed by oxidation. The process begins with the conversion of serotonin to 5-hydroxyindoleacetaldehyde, which is then oxidized to form 5-HIAA. This metabolic pathway is crucial for the regulation of serotonin levels in the body.

Clinical significance

The measurement of 5-HIAA in the urine is an important diagnostic tool. Elevated levels of 5-HIAA can indicate the presence of a carcinoid tumor, which is a type of neuroendocrine tumor that secretes large amounts of serotonin. These tumors are often found in the gastrointestinal tract and can lead to a condition known as carcinoid syndrome, characterized by flushing, diarrhea, and heart valve lesions.

Testing

Urinary 5-HIAA levels are typically measured 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

In addition to carcinoid tumors, other conditions can affect 5-HIAA levels. For example, malabsorption syndromes and liver disease can alter serotonin metabolism and subsequently affect 5-HIAA excretion. Conversely, low levels of 5-HIAA may be seen in conditions such as depression and Parkinson's disease, where serotonin metabolism is impaired.

Related pages

• Serotonin
• Carcinoid tumor
• Neurotransmitter
• Monoamine oxidase

Gallery

• Structural formula of 5-Hydroxyindoleacetic acid
  Structural formula of 5-Hydroxyindoleacetic acid