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Quality Specifications for the Determination of Copper, Zinc, and Selenium in Human Serum or Plasma: Evaluation of an Approach Based on Biological and Analytical Variation

¹ Département de Biologie Intégrée, Pôle de biologie, CHU de Grenoble, Grenoble, France; ² Centre de Toxicologie, Institut National de Santé Publique du Québec, Québec, QC Canada; ³ MCA Laboratory, Queen Beatrix Hospital, The Netherlands; ⁴ Trace Elements Laboratory, Wadsworth Center, New York State Department of Health, Albany, NY; ⁵ Institute of Occupational, Social and Environmental Medicine, University of Erlangen-Nuernberg, Erlangen, Germany; ⁶ Bureau of Quality Assurance, Scientific Institute of Public Health, Brussels, Belgium; ⁷ Higiene Industrial, Centro de Seguridad y Salud en el Trabajo, Santander, Spain; ⁸ Biomonitoring Laboratory, Finnish Institute of Occupational Health, Helsinki, Finland; ⁹ Dipartimento di Sanità Alimentare e Animale, Istituto Superiore di Sanità, Roma, Italy; ¹⁰ Centre for Clinical Science and Measurement, School of Biomedical and Life Sciences, University of Surrey, Guildford, U.K.

^aAddress correspondence to this author at: Département de Biologie Intégrée, Pôle de biologie, CHU de Grenoble, 38043 Grenoble cedex 9, France. Fax 33 4 76 76 58 21; e-mail JArnaud{at}chu-grenoble.fr.

Background: Trace element external quality assessment schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. However, monitoring of participant performance varies according to the scheme and can lead to conflicting conclusions.

Methods: Quality specifications based on biological intra- and interindividual variability were calculated and compared to those currently used by various trace element external quality assessment schemes for plasma or serum copper, zinc, and selenium concentrations. For this purpose, we evaluated results reported by participating laboratories in different schemes, at key concentrations, using z scores.

Results: Minimal quality specifications developed from the biological intra- and interindividual variability were, for Cu, ±0.84 µmol/L or 12% of the assigned target concentration, whichever is greater; for Zn, ±1.20 µmol/L or 15% of the assigned target concentration, whichever is greater; and for Se, ±0.072 µmol/L or 12% of the assigned target concentration, whichever is greater. Reported performance of the participating laboratories depended on analyte, concentration, and the selected quality specification. In addition, the most commonly used methods for the determination of Cu, Zn, and Se may give different results.

Conclusions: The proposed minimal quality specifications based on biological variation are generally slightly less stringent than those currently in use, although they do not drastically change the performance evaluation in the different schemes. These specifications are a first step in the harmonization of practices among the schemes and remain to be evaluated.