The contribution of assay variation and biological variation to the total variability of plasma HIV-1 RNA measurements

Objectives: To assess the specific contributions of assay variation and bio logical variation to the total variation of plasma HIV-1 RNA measured by th e Roche Monitor assay and the extent to which batch assays reduced both ass ay variability and total variability compared with real-time determinations . Design: A retrospective analysis of data obtained from three trials conduct ed by the Adult and Pediatric AIDS Clinical Trials Groups (ATCG), the Women and Infants Transmission Study (WITS) and the NIAID-sponsored Virology Qua lity Assurance Program. Methods: Within-subject variation was assessed from stored, serially collec ted plasma samples from 663 subjects enrolled in the ACTG and WITS studies. Interassay and intra-assay variation were estimated from two of the clinic al trials and 22 laboratories that participated in a quality assurance prog ram and were used to estimate the effect of real-time testing on total vari ation. Results: The total variation (standard deviation) from a random effects mod el was 0.26 log(10) RNA copies/ml. The estimated interassay variation was 0 .08 log(10) and intra-assay variation was 0.12 log(10) RNA copies/ml. Biolo gical variation accounted for 56-80% of total variation. The effect of real -time testing compared with batch testing was minimal. Conclusion: Our estimates of total within-subject HIV-1 RNA variation suppo rt the current recommendation to obtain at least two specimens, preferably obtained less than 2 weeks apart, for viral RNA measurement before starting therapy. The major contribution of biological variation to the total varia tion supports the use of real-time HIV-1 RNA assays, provided that consiste nt specimen collection procedures are followed and acceptable assay profici ency is maintained. (C) 1999 Lippincott Williams & Wilkins.