Experience with external quality assessment of drugs of abuse testing in the Lombardy Region in Italy.

Following up previous experience with External Quality Assessment (EQA) and Proficiency Testing Programs (PTP) on drugs of abuse (DoA) testing in Italy and in other European countries, the government of the Lombardy Region, first among Italian regions, established in 1995 a compulsory EQA scheme for laboratories authorized to perform these tests. The purpose of the present work is the description of the program and the overall evaluation of the results obtained in the first three annual cycles (1995-1998). During each annual cycle laboratories received 22 urine samples; some samples were collected from patients ("real samples") and some were "spiked" urine samples. Both types of samples could contain the following substances/classes of substances: opiates, cocaine, cannabinoids, methadone, buprenorphine, benzodiazepines, barbiturates. Type A laboratories used an immunological screening method; they expressed the results as concentrations. Type B laboratories, authorized to perform screening methods followed by confirmatory techniques, searched for and identified single substances and provided an interpretation on possibly taken drugs. During the study period the laboratories produced about 21,000 analytical results. Among them, false-negative results were 0.9% of true positives, and false-positive results were 0.7% of true negatives. Performance using the spiked samples was better than using real samples, and performance of type B laboratories better than that of type A. The results obtained during the program are consistent with those of other quality control programs. This program, in addition, has provided information on the status of DoA testing in the Lombardy region's laboratories, in particular on their analytical performance, on the quality of interpretation of results and on a degree of improvement achieved during the program.