title: Enzyme-linked immunoassay for plasma-free metanephrines in the biochemical diagnosis of phaeochromocytoma in adults is not ideal.
abstract: BACKGROUND
  The aim of the study was to define the analytical and diagnostic performance of the Labor Diagnostica Nord (LDN) 2-Met plasma ELISA assay for fractionated plasma metanephrines in the biochemical diagnosis of phaeochromocytoma.
  
  
  METHODS
  The stated manufacturer's performance characteristics were assessed. Clinical utility was evaluated against liquid chromatography tandem mass spectrometry (LC-MS/MS) using bias, sensitivity and specificity outcomes. Samples (n=73) were collected from patients in whom phaeochromocytoma had been excluded (n=60) based on low probability of disease, repeat negative testing for urinary fractionated catecholamines and metanephrines, lack of radiological and histological evidence of a tumour and from a group (n=13) in whom the tumour had been histologically confirmed. Blood collected into k(2)EDTA tubes was processed within 30 min. Separated plasma was aliquoted (×2) and frozen at -40°C prior to analyses. One aliquot was analysed for plasma metanephrines using the LDN 2-Met ELISA and the other by LC-MS/MS.
  
  
  RESULTS
  The mean bias of -32% for normetanephrine (ELISA) when compared to the reference method (LC-MS/MS) makes under-diagnosis of phaeochromocytoma likely. The sensitivity of the assay (100%) was equal to the reference method, but specificity (88.3%) lower than the reference method (95%), making it less than optimum for the biochemical diagnosis of phaeochromocytoma.
  
  
  CONCLUSIONS
  Plasma-free metanephrines as measured by Labor Diagnostica Nord (LDN) 2-Met ELISA do not display test characteristics that would support their introduction or continuation as part of a screening protocol for the biochemical detection of phaeochromocytoma unless the calibration problem identified is corrected and other more accurate and analytically specific methods remain unavailable.
authors: Department of Chemical Pathology, Beaumont Hospital, Dublin, Ireland. fiona_mullins@yahoo.ie
authors: Fiona
authors: F
authors: Mullins
authors: Paula
authors: P
authors: O'Shea
authors: Roland
authors: R
authors: FitzGerald
authors: William
authors: W
authors: Tormey
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000097:blood / Q000175:diagnosis*; D003951:Diagnostic Errors; D006801:Humans; D007124:Immunoenzyme Techniques / Q000592:standards*; D008676:Metanephrine / Q000097:blood*; D009647:Normetanephrine / Q000097:blood; D010673:Pheochromocytoma / Q000097:blood / Q000175:diagnosis*; D012372:ROC Curve; D012680:Sensitivity and Specificity
chemical_list: D009647:Normetanephrine; D008676:Metanephrine