title: Absolute CD4 T-cell counting in resource-poor settings: direct volumetric measurements versus bead-based clinical flow cytometry instruments.
abstract: Flow cytometry is an accurate but expensive method to determine absolute CD4 cell counts. We compared different methods to measure absolute CD4 counts in blood samples from HIV-infected and uninfected subjects using a research/clinical flow cytometer (FACScan); a dedicated clinical instrument (FACSCount); and a volumetric, mobile, open-system flow cytometer equipped with 3 fluorescence and 2 light scatter detectors (Cyflow SL blue). The FACScan and Cyflow were used as single-platform instruments, but they differ in running cost, which is a central factor for resource-poor settings. Direct volumetric and bead-based CD4 measurements on the Cyflow were compared with 2 bead-based single-platform CD4 measurements on the FACSCount and on FACScan (TruCount) in "Le Dantec" Hospital, Dakar, Senegal, using whole blood samples from 102 HIV+ and 28 HIV- subjects. The agreement between the various measurement methods was evaluated by Bland-Altman analysis. Volumetric CD4 measurements on the Cyflow using a no-lyse-no-wash (NLNW) procedure and a lyse-no-wash (LNW) procedure correlated well with each other (R2 = 0.98) and with CD4 measurements on the FACSCount (R2 = 0.97) and FACScan (R2 = 0.97), respectively. Red blood cell lysis had no negative effect on the accuracy of absolute CD4 counting on the Cyflow. An excellent correlation was observed between bead-based CD4 measurements on the Cyflow and CD4 measurements on the FACSCount (R2 = 0.99) and FACScan (R2 = 0.99). Rigid internal and external quality control monitoring and adequate training of technicians were considered essential to generate accurate volumetric CD4 measurements on the Cyflow.
authors.affiliation: Immunology Unit, Laboratory of Bacteriology-Virology, Cheikh Anta Diop University, Dakar, Senegal. tndieye@yahoo.co.uk
authors.forename: Tandakha Ndiaye
authors.initials: TN
authors.lastname: Dieye
authors.forename: Chris
authors.initials: C
authors.lastname: Vereecken
authors.forename: Abdoul Aziz
authors.initials: AA
authors.lastname: Diallo
authors.forename: Pascale
authors.initials: P
authors.lastname: Ondoa
authors.forename: Papa Alassane
authors.initials: PA
authors.lastname: Diaw
authors.forename: Makhtar
authors.initials: M
authors.lastname: Camara
authors.forename: Farba
authors.initials: F
authors.lastname: Karam
authors.forename: Souleymane
authors.initials: S
authors.lastname: Mboup
authors.forename: Luc
authors.initials: L
authors.lastname: Kestens
mesh_terms: D001530:Belgium; D018791:CD4 Lymphocyte Count / Q000191:economics* / Q000379:methods*; D003365:Costs and Cost Analysis; D005434:Flow Cytometry / Q000379:methods; D015658:HIV Infections / Q000097:blood* / Q000276:immunology*; D006801:Humans; D016130:Immunophenotyping / Q000379:methods; D011203:Poverty; D012016:Reference Values; D015203:Reproducibility of Results