Which of the following is not used in the evaluation of pheochromocytoma?

• A. Plasma metanephrines testing
• B. Clonidine suppression test
• C. Glucagon suppression test
• D. Serum prolactin

Answer: (D)

Pheochromocytoma evaluation focuses on detecting excess catecholamines or their metabolites. Plasma free metanephrines (or urinary fractionated metanephrines) are highly sensitive screening tests for this purpose. The clonidine suppression test is used to distinguish true catecholamine excess from stress-induced elevations by seeing if plasma norepinephrine falls after clonidine in normal individuals but not in pheochromocytoma. A glucagon-based provocative test is another tool that can help confirm pheochromocytoma by triggering a catecholamine response in suspected cases when results are uncertain. Serum prolactin, while useful for pituitary disorders, does not reflect pheochromocytoma activity and is not part of its evaluation.