[Analysis of the results of the SEIMC External Quality Control Program for HIV-1 and HCV viral loads, 2007]

Abstract

Background: Human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) viral load determinations are among the most important tasks performed in the molecular microbiology laboratory, due to their importance in patient follow-up. Quality control tools are crucial in these laboratories to ensure the accuracy of the results. This article presents the analysis of the results obtained in 2007 from the SEIMC External Quality Control Program for HIV-1 and HCV viral loads.

Methods and results: 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 a range of 2-5 log(10) copies/mL; to analyze repeatability, two of these standards were identical. The specificity was good for all the methods used by the participants, and only two out of 75 results were considered to be false positive results. A substantial proportion of the laboratories (20% 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. A few errors were due to the transcription of the analytical result. Repeatability was also acceptable but approximately 15% of laboratories failed this evaluation. The HCV program consisted of two standards with different viral load contents. Most of the participants (94.6%) obtained results within the accepted range (mean +/-1.96 SD log(10) UI/mL), and interlaboratory variability was <0.5 log units for both standards and all techniques.

Conclusions: 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 wide interlaboratory variability, the use of the same method and the same laboratory for patient follow-up is advisable.