Diagnostic efficacy of unconjugated plasma metanephrines for the detectionof pheochromocytoma

Background: Recently, measurement of plasma metanephrines was suggested to improve the detection of pheochromocytoma compared with the other common bi ochemical tests. Objective: To examine the diagnostic precision of measurements of plasma me tanephrines, plasma catecholamines, and urinary catecholamines and to asses s their variability. Methods: Plasma metanephrine as well as plasma and urinary catecholamine co ncentrations were measured by high-performance liquid chromatography with e lectrochemical detection. Before surgery, responses of plasma metanephrines and catecholamines to change of posture were determined. Intraoperatively, metanephrines and catecholamines were measured before skin incision, durin g maximal mechanical tumor manipulation, and repetitively after the tumor w as separated from the circulation. Patients were reexamined 1 months after surgery. Patients with pheochromocytoma (n=17) and with histologically prov ed other adrenal tumors (n=14) were studied before, during, and after surge ry. Results: Measurement of plasma metanephrines and plasma and urinary catecho lamines provided 100% and 82% sensitivity, respectively, for the detection of pheochromocytoma (P<.001). Levels of plasma catecholamines but not metan ephrines increased in response to change of posture (norepinephrine, P=.03; epinephrine, P=.07) and intraoperative stress (norepinephrine, P=.002; epi nephrine, 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.