[Analysis of the results of the HIV-1, HCV and HBV viral load of the SEIMC External Quality Control Program. Year 2011].

Human immunodeficiency virus type 1 (HIV-1) and hepatitis B (HBV) and 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 of the 2011 SEIMC External Quality Control Program for HIV-1, HCV, and HBV viral loads. 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 log10 copies/mL; to determine repeatability, two of these standards were identical. A significant proportion of the laboratories (52.1% on average) obtained values outside the accepted range (mean ± 0,25 log10 copies/mL), depending on the standard and on the method used for quantification. Repeatability was very good, with up to 94.9% of laboratories reporting results within the accepted range (Δ<0,5 log10 copies/ mL). The HBV and HCV program consisted of two standards with different viral load contents. In most of the participating laboratories (90% in the case of HCV and 86% in that of HBV), all the results were within the accepted range (mean ± 1.96 SD log10UI/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 the marked interlaboratory variability found, use of the same method and the same laboratory for patient follow-up is advisable.