5-Hydroxyindoleacetic acid (5-HIAA) is the primary metabolite of which neurotransmitter?

5-Hydroxyindoleacetic acid (5-HIAA) is the primary metabolite of which neurotransmitter?

• A. Epinephrine
• B. Norepinephrine
• C. Serotonin
• D. Prolactin

Answer: (C)

5-HIAA is the main breakdown product of serotonin. Serotonin is inactivated mainly by monoamine oxidase to 5-hydroxyindoleacetaldehyde, which is then converted to 5-HIAA and excreted in urine. Because urinary 5-HIAA rises with increased serotonin turnover, it’s used clinically to help diagnose conditions like carcinoid tumors. The other substances listed are handled differently: epinephrine and norepinephrine are metabolized into metanephrines and then vanillylmandelic acid, not 5-HIAA, and prolactin is a peptide hormone with a distinct metabolic pathway that doesn’t produce 5-HIAA.

5-HIAA is the main breakdown product of serotonin. Serotonin is inactivated mainly by monoamine oxidase to 5-hydroxyindoleacetaldehyde, which is then converted to 5-HIAA and excreted in urine. Because urinary 5-HIAA rises with increased serotonin turnover, it’s used clinically to help diagnose conditions like carcinoid tumors. The other substances listed are handled differently: epinephrine and norepinephrine are metabolized into metanephrines and then vanillylmandelic acid, not 5-HIAA, and prolactin is a peptide hormone with a distinct metabolic pathway that doesn’t produce 5-HIAA.