Two US FDA approved assays are commonly used for

Two US FDA-approved assays are commonly used for VL monitoring: the COBAS AmpliPrep/COBAS® Taqman® HIV-1 version 2.0 (“CAP/CTM HIV-1 v2”; Roche Molecular Systems) [18], and the RealTime HIV-1 assay (“RealTime HIV-1”, Abbott Molecular) [19]. Several studies have shown good correlation between the assays [17,20,21] with lower agreement around the LLOQ [22,23]. The cobas® HIV-1 quantitative nucleic valsartan and alcohol test for use on the cobas® 4800 system (“cobas 4800 HIV-1”, Roche Molecular Systems) is a fully automated real-time PCR-based assay, which uses a dual-target design for subtype coverage, including groups M, N and O.
Objective
Study design
Results
Discussion Results of this study demonstrate that cobas 4800 HIV-1 has high sensitivity and specificity, and can be used for HIV-1 from all major group M subtypes, group N and O. The LOD was 14.2 copies/mL (95% CI: 12.5 to 16.6 copies/mL) for the 400 μL input volume and 43.9 copies/mL (37.7 to 52.7 copies/mL) for the 200 μL input volume. The cobas 4800 HIV-1 test showed high concordance with CAP/CTM HIV-1 v2 and RealTime HIV-1. The comparison with CAP/CTM HIV-1 v2 is similar to results obtained using the cobas 6800 HIV-1 test [26], where a small (0.11 log10) difference was observed. This small difference is unlikely to be clinically significant. Test results were precise and accurate across all tested subtypes, input volumes, and VL in the linear range. The LOD of cobas 4800 HIV-1 with a low input volume of 200 μL ensures accurate quantitation near the clinically important threshold of 50 copies/mL when sample volumes are limiting, for example with pediatric samples, or when repeat testing is needed for samples with limited quantities. We observed greater variability in the difference between the cobas 4800 HIV-1 and CAP/CTM HIV-1 v2 (Fig. 2B, upper – lower 95% CI limits 1.1 log10) compared to between cobas 4800 HIV-1 and RealTime HIV-1 (Fig. 3B, upper – lower 95% CI limits 0.93 log10). While the reasons for this difference are unknown, they are unlikely to be clinically significant. The cobas 4800 HIV-1 test showed ≥96.5% agreement with the CAP/CTM HIV-1 v2 assay for categorizing VL as being above or below the 50 and 200 copies/mL thresholds. Similar levels of agreement were found between cobas 4800 HIV-1 and RealTime HIV-1. Although the use of one type of molecular platform is recommended for the follow up of VL because of the different performance characteristics of the different systems [27,28], results of Multiforked chromosome study showed improved commutability among the three assays. Highly sensitive quantitative assays are required to monitor viral suppression in patients treated with ART. Accurate quantification near clinically relevant thresholds used to define treatment success or failure is of special importance. Current thresholds for defining treatment failure are 50 copies/mL according to the European AIDS Clinical Society guidelines [29], or 200 copies/mL as defined by the US Department of Health and Human Services (DHHS) guidelines [30,31]. One reason cited for the DHHS threshold is higher assay variability at low viral load [31]. A comparison between CAP/CTM HIV-1 v2 and RealTime HIV-1 in patients on ART in two AIDS Clinical Trial Group studies demonstrated a high degree of agreement between the two assays but significantly better ability to identify virological failure reliably when defined by the higher threshold [32]. In our study, although a similarly high level of agreement between the three assays at both 50 and 200 copies/ml thresholds was also shown, no significant differences were revealed between the two thresholds. This could be explained by the lower number of samples tested, especially for the correlation between cobas 4800 HIV-1 and RealTime HIV-1. WHO recommends that national HIV programs implement VL testing for ART-treated patients biannually in the first year and annually thereafter [5]. With 21.7 million people on ART globally, meeting this goal requires significant VL testing capacity increases in laboratories in low- and middle-income countries. One part of the solution to this forecasted demand is to maximize testing throughput without a concomitant increase in the need for highly skilled laboratory workers. Medium and high-throughput automated systems such as cobas 4800 and 6800/8800 [33] may help address this need. The lower input volume of the cobas platform, acceptance of primary tubes, and the ability to test for other targets in addition to HIV-1, may be advantageous in a clinical laboratory setting [33,34].