Performance of plasma free metanephrines measured by liquid chromatography–tandem mass spectrometry in the diagnosis of pheochromocytoma

BackgroundPlasma free metanephrines have proved a highly sensitive biochemical test for the diagnosis of pheochromocytoma. We have developed and validated a simple, LC–MS/MS method to determine plasma metanephrines and compared the diagnostic efficacy of the method with an enzyme immunoassay procedure in 151 patients, 38 with histologically confirmed pheochromocytoma.MethodsOff-line solid phase extraction in a 96-well plate format was used to isolate metanephrines from 100-μL of plasma, followed by rapid separation with hydrophilic interaction chromatography. Mass spectrometry detection was performed in multiple-reaction monitoring mode using a tandem quadrupole mass spectrometer with positive electrospray ionization.ResultsDetection limits were < 0.1 nmol/l with method linearity up to 23.0 nmol/L for normetanephrine (NMN), metanephrine (MN) and 3-methoxytyramine (3-MT). Method comparison with an automated LC–MS/MS yielded Deming regression slopes of r = 0.94 for NMN, r = 0.98 for MN and r = 0.94 for 3-MT. Method comparison with enzyme immunoassay revealed regression slope of r = 1.28 (NMN) and 1.25 (MN) with values approximately 25% lower than LC–MS/MS. Plasma metanephrines by LC–MS/MS identified all 38 patients with phaeochromocytoma compared with 36 cases by immunoassay.ConclusionsPlasma metanephrines measured by LC–MS/MS are a reliable and sensitive test for the biochemical detection of pheochromocytoma.