A 48-year-old female with family history of pheochromocytoma is undergoing laparoscopic nephrectomy for newly diagnosed renal cell carcinoma. The surgeons note an adrenal mass not previously seen on imaging, and manipulation of the kidney causes severe hypertension up to 225/135 mm Hg. The case is aborted, with the patient transferred to the intensive care unit for blood pressure management. In this scenario, which of the following biochemical testing is most recommended?
A. 24-hour urine catecholaminesCorrect Answer: D
Measuring plasma-fractionated metanephrines is the recommended first-line test when there is a high index of suspicion for pheochromocytoma. It has the highest sensitivity (96%-100%) and moderate specificity (85%-91%) among all biochemical testing for pheochromocytoma, with the highest area under the receiver operating characteristic curve. The nearly maximal negative predictive value of plasma free metanephrines suggests that pheochromocytoma can be ruled out when the test result is within the normal range. However, the falsepositive rate is high when the blood is not drawn per recommendation (i.e., supine with an indwelling cannula over 30 minutes). Since plasmafractionated metanephrines is associated with a high–false-positive rate, it should only be used when there is a high index of suspicion. The following scenarios warrant a high index of suspicion: family history of pheochromocytoma, genetic syndrome that is associated with pheochromocytoma (MEN2, VHL, NF1), prior resection of pheochromocytoma, or adrenal mass consistent with pheochromocytoma. The patient above had a family history of pheochromocytoma and an incidentally found adrenal mass, which qualify for a high index of suspicion and thus further confirmation with plasma-fractionated metanephrines.
24-hour urine-fractionated metanephrines is the recommended test for patients with low index of suspicion. It has a sensitivity of 92% to 98% and a specificity of 94% to 98% and thus less sensitive than plasma metanephrines but more specific. Measurement of plasma or urinary catecholamines is less sensitive than the aforementioned tests, likely due to the sporadic secretion of parent catecholamines compared to the continuous diffusion of intratumorally produced metanephrines into the circulation.
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