External quality assessment scheme in Belgium. Heavy metal analyses.

An external quality assessment scheme for heavy metal analyses has been implemented in Belgium (quality control in Belgium, QCB) by the Epidemiology Unit of the Institute of Hygiene and Epidemiology since 1993. Aims of the scheme are to improve laboratories performances by means of interlaboratory comparisons and to provide national authority with information about the dispersion of results for heavy metal analyses in Belgium. The analytes included in the QCB are lead, cadmium and selenium in blood. Control samples are in-house prepared from human blood, spiked with appropriate amounts of Pb, Cd and Se. Four exercises are performed every year and participants receive three samples to analyze. Target values are calculated for each element from the regression lines obtained by plotting the results of a reference laboratory against the added amounts. The QCB does not yet include acceptability criteria of the results and no measures are taken against poor performers at this stage, although advice is available by personal contacts with the organisers.