The International Interlaboratory Quality Control Program for Measurement of Antiretroviral Drugs in Plasma: a global proficiency testing program.

The International Interlaboratory Quality Control Program for Measurement of Antiretroviral Drugs in Plasma was initiated in 1999 by Radboud University Nijmegen Medical Center, The Netherlands, and continued later on in collaboration with the Dutch Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology (www.kkgt.nl). The aim of this analysis was to evaluate the first 10 years of the Program and to determine variables associated with reporting of less accurate results. Two rounds are organized annually in which blind samples are shipped to participants containing a low, medium, or high concentration of each antiretroviral drug. Any reported result that deviates more than 20% from the spiked concentration is defined as inaccurate. By the end of 2009, the number of laboratories participating in the Program had increased to 56; 44 (79%) are located in Europe. A total of 12,798 test results was available for analysis, of which 2104 (16.4%) were reported as inaccurate. Performance was best for samples containing nevirapine (mean of inadequate scores per round: 11.1%) and lopinavir (11.9%) and worst for indinavir (18.7%), atazanavir (18.9%), saquinavir (19.6%), and nelfinavir (21.3%). High and medium concentrations were less frequently reported as inaccurate than low concentrations: 13.5%, 13.0%, and 22.4%, respectively. Although the overall performance of the laboratories varied per year, a trend was visible for improvement over time with 19.9% of the results being inaccurate in 2002 (n = 20 laboratories) to 15.7% in 2009 (n = 56 laboratories). The Program provides a proficiency testing program in which laboratories are alerted to potential analytical errors while performing therapeutic drug monitoring in HIV-infected patients. Laboratories should put more effort in adequately analyzing concentrations of antiretroviral drugs with low minimum effective concentrations.