Best to Diagnose Pheo

Plasma free metanephrines is the best single test to diagnose pheochromocytoma, according to a multicenter cohort study reported in the March 20 issue of The Journal of the American Medical Association.

"Plasma free metanephrines constitute the best test for excluding or confirming pheochromocytoma and should be the test of first choice for diagnosis of the tumor," write Jacques W.M. Lenders, MD, PhD, of St. Radboud University Medical Center in Nijmegen, Netherlands, and colleagues. "Combining different tests did not improve the diagnostic yield beyond that of a single test of plasma free metanephrines."

The authors compared test results in 214 patients with histologically confirmed or widely metastatic pheochromocytoma and in 644 patients not found to have this tumor on extensive workup despite suggestive signs and symptoms.

Sensitivities were 99% for plasma free metanephrines and 97% for urinary fractionated metanephrines, which were higher than those for plasma catecholamines (84%), urinary catecholamines (86%), urinary total metanephrines (77%), and urinary vanillylmandelic acid (VMA; 64%).

Specificity was highest for urinary VMA (95%) and urinary total metanephrines (93%); intermediate for plasma free metanephrines (89%), urinary catecholamines (88%), and plasma catecholamines (81%); and lowest for urinary fractionated metanephrines (69%).

Using receiver-operating characteristic analysis to consider both sensitivity and specificity, the authors concluded that plasma free metanephrines was the best test for confirming or excluding pheochromocytoma. This test was negative in more than 80% of patients tested, virtually excluding pheochromocytoma and eliminating the need for immediate further tests in these patients.

"In about 80% of patients with pheochromocytoma, the magnitude of increase in plasma free metanephrines is so large that the tumor can be confirmed with close to 100% probability," they write. "In these patients, the immediate task is to locate the tumor."

Reviewed by Gary D. Vogin, MD, MedscapeWire 2002. © 2002 Medscape Portals, Inc

Calibrations for diagnosing pheos in children have been compiled by Weise, Walther, Eisenhofer et al. "The findings indicate that plasma free metanephrines provide a sensitive tool for detection of pheochromocytoma in children. Age appropriate reference ranges should be used, and gender differences should be considered." Journal of Clinical Endocrinological Metabolism, 87(2002): 1955-1960.