Objective: To evaluate the feasibility and the relevance of the implementation of an alternative technique to flow cytometry (FC) for enumerating CD4 T cells (Dynabeads; Dynal Biotech, Oslo, Norway), based on quantifying CD4 T cells by epifluorescent microscopy following their isolation using anti-CD4 monoclonal antibody-coated magnetic beads.
Design: International multi-center study. Five consecutive runs of dual CD4 T-lymphocyte enumeration by both techniques in six sites in five countries of West Africa.
Methods: A total of 657 pairs of values of CD4 cell counts were generated by 43 technicians by both FC (TruCount; Becton Dickinson Immunocytometry Systems, San Jose, California, USA) and Dynabeads from blood samples obtained from 301 HIV-infected patients, seen in one (n = 112), two (n = 61), three (n = 75), four (n = 40) or five (n = 13) occasions.
Results: The correlation coefficient between the results of the two techniques was 0.89. The overall systematic difference between Dynabeads and FC was -16 x 10(6) cells/l (P < 10(-4)). The median difference was insignificant (+7.5 cells) for CD4 cell counts below 200 x 10(6) cells/l and increased with CD4 levels. Patients were consistently classified at the threshold of 200 x 106 cells/l by both methods in 88.7% of cases. Among the 74 discrepant pairs of values, only 31 (4.7%) exhibited a difference of more than 100 x 10(6) cells/l.
Conclusions: Results from Dynabeads and FC were highly correlated. The ability of the alternative method to consistently classify results in agreement with FC, at thresholds of CD4 cell counts relevant for clinical care, was high. The implementation of this low-cost method was easy and successful in the West African context.