Report of the Korean Association of External Quality Assessment Service on Therapeutic Drug Monitoring and Toxicology (2015–2019)

Korean Association of External Quality Assessment Service offered to conduct a proficiency test program for therapeutic drug monitoring (TDM) and testing drugs of abuse (DOA), which was named as the TDM and Toxicology program. This report summarizes the results of the proficiency tests performed between 2015–2019. In the proficiency test program, low- and high-level control materials for TDM, and positive and negative control materials for testing DOA were examined in the participating laboratories. The number of participating laboratories for TDM increased from 105 in 2015 (1st trial) to 114 in 2019 (2nd trial). Valproic acid was the most commonly tested substance. The most widely used TDM analyzer was the Architect i System (Abbott Laboratories, USA). The TDM proficiency test coefficients of variation for each test substance exhibit a broad range (0%–300%), which is mainly attributed to the test substance, concentration, or number of participating laboratories. The number of participating laboratories for DOA testing markedly increased from 35 in 2015 (1st trial) to 123 in 2019 (2nd trial). The proportion of the acceptable results ranged between 84%–100%. In 2019, five laboratories reported false negative results in the first trial, but later, they reported correct results in the second trial. In the proficiency test program for TDM and testing DOA during 2015–2019, the performance of participating laboratories was generally decent. However, continuous efforts to monitor and improve the quality of testing are required, which can happen only with increased participation in the proficiency test program.ope