title: Technical and regulatory shortcomings of the TaqMan version 1 HIV viral load assay.
abstract: BACKGROUND
  The lower limit of detection of the original Roche Amplicor HIV plasma viral load (pVL) assay (50 copies/mL) has defined HIV treatment success. The Amplicor assay, however, has been replaced by the Roche TaqMan assay(s). Changes to the limits of detection and calibration have not been validated for clinical utility. Sudden increases in the number of patients with detectable pVL have been reported following the introduction of the TaqMan version 1 assay.
  
  
  METHODS
  Between October 2009 and April 2010 all routine pVL samples from British Columbia, Canada, with 40-250 copies/mL by TaqMan were re-tested by Amplicor (N = 1198). Subsequent short-term virological and resistance outcomes were followed in patients with unchanged therapy (N = 279; median 3.2 months follow-up).
  
  
  RESULTS
  TaqMan and Amplicor values correlated poorly at low pVL values. Low-level pVL by TaqMan was not associated with impending short-term virological failure; only 17% of patients with 40-250 copies/mL by TaqMan had detectable pVL by Amplicor at follow-up. During the follow-up period only 20% of patients had an increase in pVL by TaqMan (median [IQR]: 80 [36-283] copies/mL). In addition, in ~2.4% of samples pVL was dramatically underestimated by TaqMan due to poor binding of the proprietary TaqMan primers.
  
  
  CONCLUSIONS
  The replacement of Amplicor with the TaqMan assay has altered the previously accepted definition of HIV treatment failure without any evidence to support the clinical relevance of the new definition. Given the systematic differences in measurement in the low pVL range the British Columbia HIV treatment guidelines now use a threshold of >250 copies/mL by TaqMan to define treatment failure.
authors.affiliation: BC Centre for Excellence in HIV/AIDS, St Paul's Hospital, Vancouver, Canada.
authors.forename: Chanson J
authors.initials: CJ
authors.lastname: Brumme
authors.forename: Luke C
authors.initials: LC
authors.lastname: Swenson
authors.forename: Brian
authors.initials: B
authors.lastname: Wynhoven
authors.forename: Benita
authors.initials: B
authors.lastname: Yip
authors.forename: Stuart
authors.initials: S
authors.lastname: Skinner
authors.forename: Viviane Dias
authors.initials: VD
authors.lastname: Lima
authors.forename: Julio S G
authors.initials: JS
authors.lastname: Montaner
authors.forename: P Richard
authors.initials: PR
authors.lastname: Harrigan
mesh_terms: D023241:Antiretroviral Therapy, Highly Active; D002170:Canada; D015658:HIV Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000821:virology; D006801:Humans; D011933:Reagent Kits, Diagnostic / Q000592:standards* / Q000821:virology; D019562:Viral Load / Q000379:methods / Q000592:standards*
chemical_list: D011933:Reagent Kits, Diagnostic