In a patient suspected of having pheochromocytoma, measurement of which metabolite would be most useful?

In a patient suspected of having pheochromocytoma, measurement of which metabolite would be most useful?

• A. Metanephrine
• B. Homovanillic acid
• C. 5-Hydroxyindoleacetic acid
• D. Homogentisic acid

Answer: (A)

In pheochromocytoma, the tumor metabolizes produced catecholamines into metanephrines inside the tumor cells, so these metabolites are generated continuously and show up in the blood or urine even if catecholamine release is episodic. That makes metanephrine testing, especially plasma free metanephrines or urinary fractionated metanephrines, the most sensitive and reliable marker for detecting the tumor. Other metabolites mentioned don’t fit this context: homovanillic acid is a dopamine metabolite used less commonly for this purpose, 5-hydroxyindoleacetic acid tracks serotonin metabolism and is used for carcinoid tumors, and homogentisic acid is involved in alkaptonuria and not pheochromocytoma.

In pheochromocytoma, the tumor metabolizes produced catecholamines into metanephrines inside the tumor cells, so these metabolites are generated continuously and show up in the blood or urine even if catecholamine release is episodic. That makes metanephrine testing, especially plasma free metanephrines or urinary fractionated metanephrines, the most sensitive and reliable marker for detecting the tumor.

Other metabolites mentioned don’t fit this context: homovanillic acid is a dopamine metabolite used less commonly for this purpose, 5-hydroxyindoleacetic acid tracks serotonin metabolism and is used for carcinoid tumors, and homogentisic acid is involved in alkaptonuria and not pheochromocytoma.