Diagnostic efficacy of unconjugated plasma metanephrines for the detection of pheochromocytoma

Background: Recently, measurement of plasma metanephrines was suggested to improve the detection of pheochromocytoma compared with the other common biochemical tests. Objective: To examine the diagnostic precision of measurements of plasma metanephrines, plasma catecholamines, and urinary catecholamines and to assess their variability. Methods: Plasma metanephrine as well as plasma and urinary catecholamine concentrations were measured by high-performance liquid chromatography with electrochemical detection. Before surgery, responses of plasma metanephrines and catecholamines to change of posture were determined. Intraoperatively, metanephrines and catecholamines were measured before skin incision, during maximal mechanical tumor manipulation, and repetitively after the tumor was separated from the circulation. Patients were reexamined 1 months after surgery. Patients with pheochromocytoma (n=17) and with histologically proved other adrenal tumors (n=14) were studied before, during, and after surgery. Results: Measurement of plasma metanephrines and plasma and urinary catecholamines provided 100% and 82% sensitivity, respectively, for the detection of pheochromocytoma (P<.001). Levels of plasma catecholamines but not metanephrines increased in response to change of posture (norepinephrine, P=.03; epinephrine, P=.07) and intraoperative stress (norepinephrine, P=.002; epinephrine, P=.009). Conclusions: Plasma metanephrines offer improved efficacy for the diagnosis of pheochromocytoma. Less variability in response to external factors may favor plasma metanephrines in the screening for this disease.