Which test best confirms pheochromocytoma?

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Measuring metabolites produced by catecholamines is the most reliable biochemical way to confirm pheochromocytoma, because the tumor continuously metabolizes catecholamines into metanephrines. The plasma-free metanephrines test captures these metabolites in the blood and has the highest sensitivity among available options, so a negative result effectively helps rule out pheochromocytoma. This makes it the best single test to confirm the diagnosis.

The urinary test for metanephrines and catecholamines can also detect the tumor, but it requires a proper 24-hour collection and is more prone to false positives from diet, medications, and stress, making it less ideal as the first-line confirmatory test. Relying on a single parameter like normetanephrine above a fixed threshold isn’t as dependable because thresholds vary by assay and context, leading to more false positives or negatives.

In practice, a positive plasma-free metanephrine test is followed by imaging to localize the tumor.