Proficiency Analysis of Drug Susceptibility Testing by National-Level Tuberculosis Reference Laboratories from 1995 to 2003

A proficiency review of antituberculous drug susceptibility testing (DST) was undertaken by the regional tuberculosis reference laboratories of the Western Pacific Region of WHO to evaluate the performance of national reference laboratories (NRLs) and to ensure that the results from the participating laboratories are reliable and similar. A panel of 30 Mycobacterium tuberculosis strains with various patterns of resistance to isoniazid, rifampin, ethambutol, and streptomycin was sent to the NRLs, and their DST results were analyzed by comparing them with the judicial results. The efficiency scores for each drug were 90 to 99% (mean, 95%) for isoniazid, 77 to 100% (mean, 94%) for rifampin, 82 to 97% (mean, 90%) for ethambutol, and 82 to 98% (mean, 89%) for streptomycin. Significant changes over time in the rates of accordance with the judicial results were observed for rifampin (P < 0.0001) and streptomycin (P = 0.0002), whereas no changes were observed for ethambutol (P = 0.0880). The efficiency score for isoniazid was consistently good throughout the nine rounds. As a whole, NRL02 showed the highest score (95%) in accordance rates for all drugs, while NRL03 (86%) and NRL04 (88%) ranked lowest. Continued proficiency testing with subsequent technical assistance improved the DST quality of participating laboratories, demonstrating the importance of the current WHO/IUATLD external quality assurance program for DST proficiency testing.