Quality of human immunodeficiency virus viral load testing in Australia

Abstract

This study determined the proficiencies of laboratories measuring human immunodeficiency virus type 1 (HIV-1) viral loads and the accuracies of two assays used for HIV-1 viral load measurement in Australia and investigated the variability of the new versions of these assays. Quality assessment program panels containing (i) dilutions of HIV-1 subtype B, (ii) replicates of identical samples of HIV-1 subtype B, and (iii) samples of subtype E and B were tested by laboratories. Total variability (within and between laboratories) was tested with quality control samples. The coefficients of variation (CVs) for the Roche AMPLICOR HIV-1 MONITOR version (v) 1.0 and Chiron Quantiplex bDNA 2.0 assays ranged from 53 to 87% and 22 to 31%, respectively. The widespread occurrence of invalid runs with the AMPLICOR HIV-1 MONITOR 1.0 assay was identified. The CVs of the new versions of the assays were 82 to 86% for the AMPLICOR HIV-1 MONITOR v 1.5 assay and 16 to 23% for the Quantiplex bDNA 3.0 assay. For virus dilution samples, all but 5 of 19 laboratories obtained results within 2 standard deviations of the mean. The Quantiplex bDNA 2.0 assay reported values lower than those reported by the AMPLICOR HIV-1 MONITOR version 1.0 assay for samples containing HIV-1 subtype B, whereas the reverse was true for subtype E. Identification and resolution of the problem of invalid runs markedly improved the quality of HIV-1 viral load testing. The variability observed between laboratories and between assays, even the most recent versions, dictates that monitoring of viral load in an individual should always be by the same laboratory and by the same assay. Results for an individual which differ by less than 0.5 log(10) HIV-1 RNA copy number/ml should not be considered clinically significant.

FIG. 1

Incidence of invalid runs, by lot number, as proportion of total runs (shown by the number within each bar) of the AMPLICOR HIV-1 MONITOR assay in all laboratories performing HIV viral load testing in Australia. ∗, P < 0.05.

FIG. 2

Results obtained by individual laboratories, identified by code number, for QAP panel VLQA 97-1, a panel of samples with a range of HIV-1 dilutions. The panel contained an undiluted sample (●), a 1/5 dilution of a sample (▴), and a 1/25 dilution of a sample in duplicate, shown as the average (■). Data are presented as residuals (difference of the reported value from the mean). The mean is indicated by the horizontal line, and 2 SDs above and below the mean are shown by the shaded region. (A) AMPLICOR HIV-1 MONITOR assay; (B) Quantiplex bDNA assay.

FIG. 3

Results obtained by individual laboratories, identified by code number, for QAP panel VLQA 98-1, a panel of replicates of HIV-1 QC samples QC105, QC105C, and QC106. The mean is indicated by the horizontal line, and 2 SDs above and below the mean are shown by the shaded region. (A and B) Data for QC105 and QC106, respectively, obtained by the AMPLICOR HIV-1 MONITOR assay; (C and D) data for QC105C and QC106, respectively, obtained by the Quantiplex bDNA assay. Note the 10-fold difference in scale between panels B and D (results for QC106).