Trace elements in body fluids: external quality assessment scheme in The Netherlands.

External quality assessment schemes (EQAS) for trace elements in body fluids are organized in The Netherlands by the SKZL (Foundation for Quality Assessment in Clinical Laboratories). Medical laboratories participate on a voluntary base. The EQAS is designed to evaluate laboratory performance in terms of accuracy, precision and linearity. Laboratory-made frozen samples of whole blood, serum and urine, enriched with the elements of interest, i.e. Tl, Cd, Co, Hg, Se, Pb, Mg, Li, Al, Cu, Zn and As, are used. The present state of art shows an acceptable mean recovery, intra-laboratory variation and linearity. Interlaboratory variation, comparability of reference ranges and criteria of interpretation used in different laboratories are less satisfying and require improvement.