New BD FACSCount™ CD4 reagent system for simultaneous enumeration of percent and absolute CD4 T-lymphocytes in HIV-1-infected pediatric patients

BACKGROUND: Absolute CD4+ T-lymphocyte counts are used in the initiation and monitoring of antiretroviral therapy in HIV-infected patients. Becton Dickinson's (BD) FACSCount system was introduced 12 years ago as a dedicated instrument for enumeration of absolute CD4+ T-lymphocytes. However, this system does not provide percent CD4+ T-lymphocyte that is the required monitoring parameter in pediatric patients. We evaluated a new BD FACSCount CD4 software and reagents for simultaneous percent and absolute CD4+ T-lymphocytes in HIV-infected blood. METHODS: Percent and absolute CD4+ T-lymphocytes in 149 HIV-infected blood samples were determined using a new FACSCount system. Results of percent and absolute CD4+ T-lymphocytes were compared between the dual-platform (DP) method, using BD FACScan flow cytometer plus hematology analyzer and the standard FACSCount system. Correlation and agreement were analyzed using linear regression and Bland-Altman analysis. RESULTS: Percent CD4+ T-lymphocyte values obtained from the new FACSCount system correlated well with DP FACScan method (r2 = 0.977, P < 0.0001). Mean bias was only -0.36% [limit of agreement (LOA): -2.52% to +1.80%] and percent similarity was 101.36%. For absolute CD4+ T-lymphocyte, the new system correlated highly with standard FACSCount system (r2 = 0.986, P < 0.0001), with a percent similarity of 98.2. Mean bias was +3.39 cells/microl with LOA of -52.53 cells/mul to +59.31 cells/microl. CONCLUSION: This new FACSCount system is a simple and reliable system for enumeration of absolute and percent CD4+ T-lymphocytes. Having one system giving both results should reduce the cost and thus increase access to CD4 testing for pediatric and adult patients.