Results of the Abbott RealTime HIV-1 assay for specimens yielding "target not detected" results by the Cobas AmpliPrep/Cobas TaqMan HIV-1 Test

Increased risk of virologic rebound in patients on antiviral therapy with a detectable HIV load <48 copies/mL

We investigated the independent effects of HIV-1 "target not detected" measurements versus those that were detectable but below the limit of quantification by Taqman RT-PCR assay on subsequent viral rebound as there are conflicting data regarding the clinical implications of arbitrary or isolated low-level viremia. Cox proportional hazard regression modeling was used to investigate the independent effects of the first HIV-1 load measurement after introduction of the Taqman RT-PCR assay (time-point 0 [T0]), pre-T0 viral loads, CD4 T cell count, race/ethnicity, gender, age and NNRTI use on risk of a confirmed VL >50, >200, >400 and >1000 copies/mL at 22 months follow-up in analyses of all patients and propensity-matched baseline cohorts. 778 patients had a viral load that was either not detected by RT-PCR (N = 596) or detectable, but below the limit of quantification (N = 182) at T0. Detectable viremia, lower T0 CD4 count, decreased age, and having detectable or unknown VL within a year prior to T0 were each associated with viral rebound to >50, >200 and >400 copies/mL. Overall failure rates were low and <5.5% of all patients had confirmed VL >1000 copies/mL. A majority of patients with rebound >200 copies/mL subsequently re-suppressed (28 of 53). A detectable VL <48 copies/mL was independently and significantly associated with subsequent viral rebound, and is cause for clinical concern.

Large-scale comparison of Roche Cobas AmpliPrep/Cobas TaqMan and Abbott RealTime HIV assays

Significant underquantitation of HIV RNA has been reported with the Roche Cobas AmpliPrep/Cobas TaqMan HIV Test (Version 1) compared to other assays. However, these studies have generally involved limited numbers of samples from select patient populations or analysis of samples that were undetectable in the TaqMan assay. Random plasma samples submitted from throughout the United States for HIV RNA quantitation (n=1263) were compared in the Roche TaqMan and Abbott RealTime assays. Twenty-four samples (1.9%) were discrepant, with a maximum difference between the two assays of 1.9logcopies/mL. These data indicate that both tests may be susceptible to underquantitation, but the incidence is low in this large cohort of samples from across the United States.

Current challenges to viral load testing in the context of emerging genetic diversity of HIV-1

INTRODUCTION

One of the major characteristics of HIV-1 is its extreme genetic diversity. A key factor in assessing the sensitivity of a molecular-based assay measuring HIV-1 RNA viral load (VL) in plasma is its ability to detect/quantify all (or most of) relevant HIV-1 genetic subtype/recombinant forms accurately.

AREAS COVERED

This review provides an overview of the current commercially available quantitative real-time assays (the Abbott RealTime HIV-1, Roche TaqMan HIV-1 versions 1.0 and 2.0, BioMérieux Nuclisens EasyQ HIV-1, Siemens VERSANT HIV-1 RNA 1.0 kinetic PCR, and Biocentric Generic HIV Viral Load assays). For each assay, studies from 2005 to 2010 assessing the impact of HIV-1 genetic diversity on the reliability of HIV-1 RNA quantification are described.

EXPERT OPINION

In light of HIV-1 genetic diversity, a general recommendation to favor one test over the other cannot categorically be made. Larger field evaluations of HIV-1 RNA assays should be conducted in areas where HIV-1 genetic diversity is the highest. The large-scale implementation of HIV-1 VL testing is urgently required in the developing world to change HIV infection from a likely death sentence into a manageable chronic infection, as done in Northern countries.