CD4+ T-lymphocyte enumeration with a flow-rate based method in three flow cytometers with different years in service
Kovit Pattanapanyasat1, Pattamawan Chimma, Panudda Sratongno
1Office for Research and Development, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand. grkpy@mahidol.ac.th
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).
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.
