Plasma free metanephrines are superior to urine and plasma catecholamines and urine catecholamine metabolites for the investigation of phaeochromocytoma

SummaryAimTo compare the relative diagnostic efficacy of several different tests used to establish a diagnosis of phaeochro- mocytoma, in patients with a proven diagnosis of phaeo- chromocytoma, and in hospital patients with significant disease of other types.MethodsWe prospectively compared biochemical markers of catecholamine output and metabolism in plasma and urine in 22 patients with histologically proven phaeochromocytoma, 15 intensive care unit (ICU) patients, 30 patients on chronic haemodialysis and both hypertensive (n = 10) and normotensive (n = 16) controls.ResultsReceiver operating characteristic curves were plotted. At the point of maximum efficiency, plasma free metanephrines showed 100% sensitivity and 97.6% specifi- city, compared with plasma catecholamines (78.6% and 70.7%), urine catecholamines (78.6% and 87.8%), urine metanephrines (85.7% and 95.1%), and urine hydroxymethox- ymandelic acid (HMMA or VMA) (93.0% and 75.8%). All patients with phaeochromocytoma had plasma free meta nephrine concentrations at least 27% above the upper limit of the reference range. Only three other patients (two on haemodialysis and one in ICU) had PFM concentrations more than 50% above the upper limit of the reference rangeConclusionsIn patients with phaeochromocytoma, plasma free metanephrines displayed superior diagnostic sensitivity and specificity compared with other biochemical markers of catecholamine output and metabolism.