[Interlaboratory serum copper-zinc comparisons. Analytical performance during the first year].

In 1988 the Trace Elements Commission of the French Society for Clinical Biology operated an interlaboratory comparison program for copper and zinc determination in serum. The main objective is to enable participants to maintain or improve the accuracy of their analytical performance by comparing their results periodically, on the basis of three criteria: comparison of the results with the mean value, accuracy (recovery of copper and zinc additions), between-run reproducibility for identical samples. The statistical methods for evaluation are reported in detail. After one year, the results show a regular improvement in their homogeneity, especially for copper, indicating that the participants have taken into account their results to improve their analytical performance. The recovery of the copper and zinc additions shown a considerable improvement of their homogeneity. The coefficients of variation improved from 30 to 21 p. cent for copper and from 29 to 15 p. cent for zinc. The between-run reproducibility for identical samples was also evaluated. A performance score for each participant was calculated for each evaluation criteria, and a global score was attributed. The procedure for individual and global evaluation was reported in detail. The best scores were obtained for accuracy and the worst for the comparison with the mean value. The participants were considered "good", "acceptable" or "inadequate" in view of their global scores. The global performance was compared to other international interlaboratory comparison programs for copper and zinc in serum.