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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

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Enzyme-linked immunoassay for plasma-free metanephrines in the biochemical diagnosis of phaeochromocytoma in adults is not ideal

1 / Paula O’Shea2 / Roland FitzGerald1 / William Tormey1, 3

1Department of Chemical Pathology, Beaumont Hospital, Dublin, Ireland

2Department of Clinical Biochemistry, Galway University Hospital, Galway, Ireland

3School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland

Corresponding author: Fiona Mullins, Department of Chemical Pathology, Beaumont Hospital, Beaumont Road, Dublin 9, Ireland Phone: +353 1 8092668, Fax: +353 1 8092435

Citation Information: Clinical Chemistry and Laboratory Medicine. Volume 50, Issue 1, Pages 105–110, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: 10.1515/cclm.2011.742, October 2011

Publication History

Received:
2011-07-07
Accepted:
2011-09-20
Published Online:
2011-10-08

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 k2EDTA 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.

Keywords: bias; fractionated plasma metanephrines; immunoassay; mass spectrometry; phaeo­chromocytoma; sensitivity; specificity

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