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5-Hydroxyindoleacetic acid

Synonyms: 2-(5-Hydroxy-1H-indol-3-yl)acetic acid, 5-HIAA
German: 5-Hydroxyindolylessigsäure

1 Definition

5-Hydroxyindoleacetic acid, 5-HIAA for short, is a metabolite of serotonin. The substance is important for laboratory diagnostics because the serotonin level can be indirectly determined from the 5-HIAA concentration.

2 Chemistry

The chemical molecular formula of 5-HIAA reads:

  • C10H9NO3

The systematic term according to IUPAC is 2-(5-Hydroxy-1H-indol-3-yl)acetic acid. At room temperature, 5-HIAA is in a solid state and has a dark red to violet color. Its melting point is 162-165°C (324-329 F).

3 Laboratory medicine

5-Hydroxyindoleacetic acid is used to determine kinds of carcinoid tumors that stem from enterochromaffin cells of the small intestine. Those tumors release vast amounts of serotonin into the blood. For this, the 5-HIAA concentration in a 24-hour urine collection is determined. The urine sample has to be acidified to a pH value of below 3. The normal value for 5-HIAA excretion in urine is 2 to 6 mg per 24 hours. Values greater than 25 mg in 24 hours are a clear indication of a carcinoid tumor.

The measurement can be affected by restricted kidney function and various drugs and foods.

4 Further clinical relevance

A reduced 5-HIAA liquor concentration has been shown to correlate with aggressive behavior in children and violent suicide attempts in adults.

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