[Analysis of the results of the HIV-1 and HCV viral load of the SEIMC External Quality Control Program. Year 2009].

Human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) viral load determinations are among the most important markers in the follow-up of patients infected with these viruses. External quality control tools are crucial to ensure the accuracy of the results obtained by microbiology laboratories. This article summarizes the results obtained from the SEIMC's External Quality Control Program for HIV-1 and HCV viral loads in 2009. In the HIV-1 program, a total of five standards were sent. One standard consisted of seronegative human plasma, while the remaining four contained plasma from three different viremic patients, in the range of 2-5 log(10) copies/mL; two of these standards were identical, aiming to determine repeatability. A significant proportion of the laboratories (21.5% on average) obtained values outside the accepted range (mean ± 0.2 log(10) copies/mL), depending on the standard and on the method used for quantification. Repeatability was very good, with up to 95 % of laboratories reporting results within the accepted limits (Δ<0.5 log10 copies/mL). Post-analytical errors due to mistranscription of the results were detected for HIV-1. The HCV program consisted of two standards with different viral load contents. Most of the participants (79.7%) obtained results within the accepted range (mean ± 1.96 SD log(10) UI/mL). Data from this analysis reinforce the utility of proficiency programs to ensure the quality of the results obtained by a particular laboratory, as well as the importance of the post-analytical phase in overall quality. Due to marked interlaboratory variability, use of the same method and the same laboratory for patient follow-up is advisable.