Findings of an external quality assessment scheme for determining aluminum in dialysis fluids and water.

The analytical performance of laboratories participating in the dialysis fluids and water aluminum program of the Guildford External Quality Assessment Scheme over the period 1986-1993 has been reviewed. For aluminum concentrations > 3.33 mumol/L in dialysis fluids, the between-laboratory CV has fallen from approximately 36% to 23%, whereas for specimens of water the reduction was from 36% to approximately 18%. Improvements at lower concentrations were less impressive. Performance of individual participants varied; only a few consistently provided accurate results. Many of the participants are able to measure serum aluminum well, so lack of expertise is not responsible for poor results. We suggest that matrix effects associated with different specimen types have a significant influence on performance and that due account is not always taken of these factors. Resolution of these problems would be aided by appropriate reference materials.