title: CD4+ T-lymphocyte enumeration with a flow-rate based method in three flow cytometers with different years in service.
abstract: BACKGROUND
  CD4(+) T-lymphocyte count remains the most important surrogate marker for management of HIV patients in resource-poor countries. The standard single-platform (SP) bead-based flow cytometric method for CD4(+) testing is expensive; more affordable methods are needed. We evaluated the SP flow-rate-based calibration method for determining CD4(+) counts, using three flow cytometers of varying ages.
  
  
  METHODS
  CD4(+) counts from 103 HIV-1 infected Thai patients were determined using a SP flow-rate method in flow cytometers with 2, 12, and 16 years of service. Results were compared to the bead-based method. Correlation and agreement were analyzed using linear regression and Bland-Altman analysis.
  
  
  RESULTS
  Counts obtained from the flow-rate approach in each flow cytometer showed strong correlation with the bead-based method (R(2) = 0.97, 0.97, and 0.96 for the 2-, 12-, and 16-year-old flow cytometers). The mean biases for the flow-rate approach compared with the bead-based method were +32.4 cells/microL (limit of agreement (LOA): -83.0 to +147.8 cells/microL), -28.8 cells/microL (LOA: -131.6 to +74.1 cells/microL), and -27.0 cells/microL (LOA: -149.4 to +95.4 cells/microL).
  
  
  CONCLUSIONS
  The flow-rate approach is reliable for determining CD4(+) counts. Results do not vary by age of flow cytometer. This approach provides a cost-effective alternative for HIV patient monitoring in resource-poor settings.
authors.affiliation: Office for Research and Development, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand. grkpy@mahidol.ac.th
authors.forename: Kovit
authors.initials: K
authors.lastname: Pattanapanyasat
authors.forename: Pattamawan
authors.initials: P
authors.lastname: Chimma
authors.forename: Panudda
authors.initials: P
authors.lastname: Sratongno
authors.forename: Surada
authors.initials: S
authors.lastname: Lerdwana
mesh_terms: D018791:CD4 Lymphocyte Count; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology*; D005434:Flow Cytometry / Q000295:instrumentation* / Q000379:methods*; D015658:HIV Infections / Q000276:immunology; D006801:Humans; D012044:Regression Analysis