Measurements of plasma metanephrines by immunoassay vs liquid chromatography with tandem mass spectrometry for diagnosis of pheochromocytoma

Abstract

BackgroundReports conflict concerning measurements of plasma metanephrines (MNs) for diagnosis of pheochromocytomas/paragangliomas (PPGLs) by immunoassays compared with other methods. We aimed to compare the performance of a commercially available enzyme-linked immunoassay (EIA) kit with liquid chromatography–tandem mass spectrometric (LC–MS/MS) measurements of MNs to diagnose PPGLs.MethodsIn a substudy of a prospective, multicenter trial to study the biochemical profiles of monoamine-producing tumors, we included 341 patients (174 males and 167 females) with suspected PPGLs (median age 54 years), of whom 54 had confirmed PPGLs. Plasma MNs were measured by EIA and LC–MS/MS, each in a specialized laboratory.ResultsPlasma normetanephrine (NMN) and MN were measured 60 and 39% lower by EIA than by LC–MS/MS. Using upper cut-offs stipulated for the EIA, diagnostic sensitivity was only 74.1% at a specificity of 99.3%. In contrast, use of similar cut-offs for MN and overall lower age-adjusted cut-offs for NMN measured by LC–MS/MS returned a diagnostic sensitivity and specificity of 98.1 and 99.7%. Areas under receiver-operating characteristic curves, nevertheless, indicated comparable diagnostic performance of the EIA (0.993) and LC–MS/MS (0.985). Diagnostic sensitivity for the EIA increased to 96.2% with a minimal loss in specificity (95.1%) following use of cut-offs for the EIA adapted to correct for the negative bias.ConclusionsThe EIA underestimates plasma MNs and diagnostic sensitivity is poor using commonly stipulated cut-offs, resulting in a high risk for missing patients with PPGLs. Correction of this shortcoming can be achieved by appropriately determined cut-offs resulting in comparable diagnostic performance of EIA and LC–MS/MS assays.