Proficiency testing on drugs of abuse: one year's experience in Spain.

The need for external quality control for drugs-of-abuse urinalysis has long been recognized. Based on experiences in other countries, a proficiency testing program has been introduced recently in Spain. Sterile urine samples containing different concentrations of drugs and metabolites are analyzed by participating laboratories four times a year. Comprehensive educational reports reviewed by an advisory committee are released after each batch analysis. The first year's results verify (a) a beneficial influence of the program in regard to reducing errors when adequate techniques are used, (b) the need for using confirmatory techniques, and (c) the importance of experience and laboratory resources for optimizing results. The educational aspects of the program for the second year are stressing especially the in situ training of analysts and the supply of solutions of drugs and metabolites to be used as reference standards.