title: Utility of CD4 cell counts for early prediction of virological failure during antiretroviral therapy in a resource-limited setting.
abstract: BACKGROUND
  Viral load monitoring is not available for the vast majority of patients receiving antiretroviral therapy in resource-limited settings. However, the practical utility of CD4 cell count measurements as an alternative monitoring strategy has not been rigorously assessed.
  
  
  METHODS
  In this study, we used a novel modelling approach that accounted for all CD4 cell count and VL values measured during follow-up from the first date that VL suppression was achieved. We determined the associations between CD4 counts (absolute values and changes during ART), VL measurements and risk of virological failure (VL > 1,000 copies/ml) following initial VL suppression in 330 patients in South Africa. CD4 count changes were modelled both as the difference from baseline (DeltaCD4 count) and the difference between consecutive values (CD4 count slope) using all 3-monthly CD4 count measurements during follow-up.
  
  
  RESULTS
  During 7093.2 patient-months of observation 3756 paired CD4 count and VL measurements were made. In patients who developed virological failure (n = 179), VL correlated significantly with absolute CD4 counts (r = - 0.08, P = 0.003), DeltaCD4 counts (r = - 0.11, P < 0.01), and most strongly with CD4 count slopes (r = - 0.30, P < 0.001). However, the distributions of the absolute CD4 counts, DeltaCD4 counts and CD4 count slopes at the time of virological failure did not differ significantly from the corresponding distributions in those without virological failure (P = 0.99, P = 0.92 and P = 0.75, respectively). Moreover, in a receiver operating characteristic (ROC) curve, the association between a negative CD4 count slope and virological failure was poor (area under the curve = 0.59; sensitivity = 53.0%; specificity = 63.6%; positive predictive value = 10.9%).
  
  
  CONCLUSIONS
  CD4 count changes correlated significantly with VL at group level but had very limited utility in identifying virological failure in individual patients. CD4 count is an inadequate alternative to VL measurement for early detection of virological failure.
authors.affiliation: The Desmond Tutu HIV Centre, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa. motasimb@hotmail.com
authors.forename: Motasim
authors.initials: M
authors.lastname: Badri
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Lawn
authors.forename: Robin
authors.initials: R
authors.lastname: Wood
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000627:therapeutic use*; D018791:CD4 Lymphocyte Count; D004359:Drug Therapy, Combination; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000276:immunology* / Q000821:virology; D015497:HIV-1 / Q000187:drug effects / Q000502:physiology; D006295:Health Resources / Q000600:supply & distribution; D006801:Humans; D008297:Male; D011203:Poverty; D018894:Reverse Transcriptase Inhibitors / Q000627:therapeutic use*; D013019:South Africa; D017211:Treatment Failure; D019562:Viral Load
chemical_list: D019380:Anti-HIV Agents; D018894:Reverse Transcriptase Inhibitors