The quality of analytical determinations of copper and zinc in serum. A collaborative study in a sample of Italian laboratories.

An external quality assurance scheme for Cu and Zn analysis in serum was carried out in Italy between 1989 and 1990. It included: preparation of control materials by the organizing centre; distribution of control samples to the participants according to a random selection; elaboration of results and evaluation of laboratory performance. Inter-laboratory variability was 16.9% and 16.4%, at concentrations of 0.94 and 1.08 mg/l, for Cu and Zn, respectively. Laboratory performance in terms of percentage of results within the limits of acceptability, improved for Cu, but not for Zn analysis.