CD4+ T-lymphocyte enumeration with a flow-rate based method in three flow cytometers with different years in service

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/mu L (limit of agreement (LOA): -83.0 to +147.8 cells/mu L), -28.8 cells/mu L (LOA: -131.6 to +74.1 cells/mu L), and -27.0 cells/mu L (LOA: -149.4 to +95.4 cells/mu L). Conclusion: 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. (C) 2008 Clinical Cytometry Society.