title: HIV-1 low-level viraemia assessed with 3 commercial real-time PCR assays show high variability.
abstract: BACKGROUND
  Current real-time PCR-based HIV-1 viral load (VL) assays allow the detection of residual viraemia in antiretroviral-treated patients. The clinical outcome of HIV1 patients experiencing low-level replication (<50 cop/mL) in comparison with fully suppressed patients is currently debated. We analysed variability of 3 VL assays <50 cop/mL, and evaluated the reproducibility of viral blips <100 cop/mL.
  
  
  METHODS
  Three commercial VL assays were tested: Versant HIV-1 RNA 1.0 kPCR (Siemens), Abbott Realtime HIV-1, and Cobas Ampliprep/Cobas Taqman HIV-1 v2.0 (Roche). Ten replicates of a reference sample at 4 low target dilutions were tested to evaluate assay variability. Prospective collection of 181 clinical samples with detectable VL <50 cop/mL was used to evaluate intra-and inter-assay variability by triplicate testing. Samples from 26 patients experiencing a viral blip were retested.
  
  
  RESULTS
  All assays showed substantial variability at low VL level: the coefficient of variation at 100, 50, 25 and 12 cop/mL ranged respectively from 32 to 44%, 35 to 68%, 41 to 83% and 33 to 77%. In the intra-assay evaluation of repeatability, 52.5 to 57.5% of detectable VL <50 cop/mL tested in triplicate showed at least one fully undetected result. Variability was similar in the inter-assay arm. The VL blips could only be reproduced in 19% of cases.
  
  
  CONCLUSIONS
  The most recent versions of widespread commercial VL assays showed substantial variability at low levels and residual viraemia could not be consistently reproduced. Patient outcome studies comparing residual VL to full suppression are therefore biased when using commercial assays.
authors.affiliation: UCLouvain, AIDS Reference Laboratory, Avenue Hippocrate 54 - B1.54.05, 1200 Brussels, Belgium. jean.ruelle@uclouvain.be
authors.forename: Jean
authors.initials: J
authors.lastname: Ruelle
authors.forename: Laurent
authors.initials: L
authors.lastname: Debaisieux
authors.forename: Ellen
authors.initials: E
authors.lastname: Vancutsem
authors.forename: Annelies
authors.initials: A
authors.lastname: De Bel
authors.forename: Marie-Luce
authors.initials: ML
authors.lastname: Delforge
authors.forename: Denis
authors.initials: D
authors.lastname: Piérard
authors.forename: Patrick
authors.initials: P
authors.lastname: Goubau
mesh_terms: D016903:Drug Monitoring / Q000379:methods*; D015658:HIV Infections / Q000188:drug therapy / Q000821:virology*; D015497:HIV-1 / Q000302:isolation & purification*; D006801:Humans; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019562:Viral Load / Q000379:methods*