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.
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 micromol/L or 12% of the assigned target concentration, whichever is greater; for Zn, +/-1.20 micromol/L or 15% of the assigned target concentration, whichever is greater; and for Se, +/-0.072 micromol/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.
Arnaud
Josiane
J
Département de Biologie Intégrée, Pôle de biologie, CHU de Grenoble, Grenoble, France. JArnaud@chu-grenoble.fr
Weber
Jean-Philippe
JP
Weykamp
Cas W
CW
Parsons
Patrick J
PJ
Angerer
Jurgen
J
Mairiaux
Eric
E
Mazarrasa
Olav
O
Valkonen
Sinikka
S
Menditto
Antonio
A
Patriarca
Marina
M
Taylor
Andrew
A
D003300:Copper / Q000097:blood*; D006801:Humans; D011786:Quality Control; D015203:Reproducibility of Results; D012643:Selenium / Q000097:blood*; D013054:Spectrophotometry, Atomic / Q000379:methods* / Q000592:standards; D015032:Zinc / Q000097:blood*
D003300:Copper; D012643:Selenium; D015032:Zinc