title: CD4 enumeration technologies: a systematic review of test performance for determining eligibility for antiretroviral therapy.
abstract: BACKGROUND
  Measurement of CD4+ T-lymphocytes (CD4) is a crucial parameter in the management of HIV patients, particularly in determining eligibility to initiate antiretroviral treatment (ART). A number of technologies exist for CD4 enumeration, with considerable variation in cost, complexity, and operational requirements. We conducted a systematic review of the performance of technologies for CD4 enumeration.
  
  
  RESULTS
  Studies were identified by searching electronic databases MEDLINE and EMBASE using a pre-defined search strategy. Data on test accuracy and precision included bias and limits of agreement with a reference standard, and misclassification probabilities around CD4 thresholds of 200 and 350 cells/μl over a clinically relevant range. The secondary outcome measure was test imprecision, expressed as % coefficient of variation. Thirty-two studies evaluating 15 CD4 technologies were included, of which less than half presented data on bias and misclassification compared to the same reference technology. At CD4 counts <350 cells/μl, bias ranged from -35.2 to +13.1 cells/μl while at counts >350 cells/μl, bias ranged from -70.7 to +47 cells/μl, compared to the BD FACSCount as a reference technology. Misclassification around the threshold of 350 cells/μl ranged from 1-29% for upward classification, resulting in under-treatment, and 7-68% for downward classification resulting in overtreatment. Less than half of these studies reported within laboratory precision or reproducibility of the CD4 values obtained.
  
  
  CONCLUSIONS
  A wide range of bias and percent misclassification around treatment thresholds were reported on the CD4 enumeration technologies included in this review, with few studies reporting assay precision. The lack of standardised methodology on test evaluation, including the use of different reference standards, is a barrier to assessing relative assay performance and could hinder the introduction of new point-of-care assays in countries where they are most needed.
authors: London School of Hygiene and Tropical Medicine, London, WC1E 7HT, England.
authors: Rosanna W
authors: RW
authors: Peeling
authors: London School of Hygiene and Tropical Medicine, London, WC1E 7HT, England.
authors: Kimberly A
authors: KA
authors: Sollis
authors: London School of Hygiene and Tropical Medicine, London, WC1E 7HT, England.
authors: Sarah
authors: S
authors: Glover
authors: Centre for Biomedical Research, Burnet Institute, Melbourne, 3004, Victoria, Australia.
authors: Suzanne M
authors: SM
authors: Crowe
authors: Department of Immunology/Microbiology, Rush University Medical Center, Chicago, IL, 60612, United States of America.
authors: Alan L
authors: AL
authors: Landay
authors: Pangaea Global AIDS Foundation, Oakland, CA, 94607, United States of America.
authors: Ben
authors: B
authors: Cheng
authors: UK NEQAS for Leucocyte Immunophenotyping, Sheffield, S10 2QD, England.
authors: David
authors: D
authors: Barnett
authors: Duke Human Vaccine Institute and Center for HIV/AIDS, Immunology and Virology Quality Assessment Center, Durham, NC, 27710, United States of America.
authors: Thomas N
authors: TN
authors: Denny
authors: Division of AIDS, STD, &TB Laboratory Research, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, 30333, United States of America.
authors: Thomas J
authors: TJ
authors: Spira
authors: University of the Witwatersrand, Parktown, 2193, South Africa.
authors: Wendy S
authors: WS
authors: Stevens
authors: Director Health Programs, ELMA Philanthropies, New York, NY, United States of America.
authors: Siobhan
authors: S
authors: Crowley
authors: Clinton Health Access Initiative, Boston, MA, 02127, United States of America.
authors: Shaffiq
authors: S
authors: Essajee
authors: World Health Organization, Geneva, Switzerland.
authors: Marco
authors: M
authors: Vitoria
authors: World Health Organization, Geneva, Switzerland.
authors: Nathan
authors: N
authors: Ford
mesh_terms: D044966:Anti-Retroviral Agents / Q000627:therapeutic use*; D018791:CD4 Lymphocyte Count / Q000295:instrumentation / Q000379:methods*; D015658:HIV Infections / Q000097:blood* / Q000188:drug therapy*; D015497:HIV-1; D006801:Humans; D016239:MEDLINE; D012680:Sensitivity and Specificity
chemical_list: D044966:Anti-Retroviral Agents