Evaluation of the Partec flow cytometer against the BD FACSCalibur system for monitoring immune responses of human immunodeficiency virus-infected patients in Zimbabwe

Abstract

A single-platform volumetric flow cytometer, the Partec Cyflow SL_3, was evaluated against a BD FACSCalibur/Sysmex XT1800i dual platform for measuring CD4(+) lymphocytes, total lymphocytes, and the percentage of CD4 lymphocytes in whole-blood samples for monitoring the immune systems of human immunodeficiency virus (HIV)/AIDS patients. Statistical analyses for precision, correlation, and agreement were performed. Coefficients of variation (CV) of 5.8, 4.6, and 3.9% were obtained for low, medium, and high CD4(+) cell counts, respectively, using the SL_3, and CV of 3.7, 4.0, and 0.94 were obtained for the same categories, using the BD FACSCalibur. Significant correlations (P < 0.005) between the two assays for CD4 counts, total lymphocyte counts, and percentages of CD4 were obtained, with correlation coefficients of 0.99, 0.96, and 0.99, respectively (n = 229). Using the Bland-Altman plot, mean biases of -18 cell/microl (95% confidence interval (CI); -91 to 54 cells/microl), -0.8% (95% CI; -3.6 to 2%), and -36.8 cells/microl (95% CI; -477 to 404 cells/microl) were obtained for comparisons of CD4 counts, percentages of CD4 cells, and total lymphocyte counts, respectively. The effects of the age of the samples on the three parameters were also analyzed by comparing results from the same samples analyzed at 6, 24, and 48 h after collection. The correlation coefficients for comparisons among different time points for the same machine and among all the time points for the two different machines were greater than 0.90. These data showed that the Partec Cyflow SL_3 assay is comparable to the BD FACSCalibur/Sysmex XT1800i dual-platform method for measuring the amount of CD4(+) cells and total lymphocytes and the percentages of CD4 cells in blood samples for the purpose of monitoring HIV/AIDS patients.

FIG. 1.

A comparison of absolute CD4 counts, as determined by the Partec Cyflow SL_3 and BD FACSCalibur/Sysmex XT1800i dual-platform system through (a) correlation analyses of the results and (b) Bland-Altman bias plots illustrating a bias of −18 cells/μl (95% CI, −91 to 55). r², correlation coefficient; sd, 0.007.

FIG. 2.

A comparison of total lymphocyte counts, as determined by the Partec Cyflow SL_3 and BD FACSCalibur/Sysmex XT1800i dual-platform system through (a) correlation analyses of the results and (b) Bland-Altman bias plots illustrating a bias of −37 cells/μl (95% CI, −477 to 404). r², correlation coefficient; sd, 0.013.

FIG. 3.

A comparison the percentages of CD4 lymphocytes in the blood, as determined by the Partec Cyflow SL_3 and BD FACSCalibur/Sysmex XT1800i dual-platform system through (a) correlation analyses of the results and (b) Bland-Altman bias plots illustrating a bias of −0.8% (95% CI, −3.6 to 2.0). r², correlation coefficient; sd, 0.007.

FIG. 4.

Effect of sample age on analyses by the two methods. The tables show correlation coefficients from multiple cross-correlation analyses of data from the analysis of sample age on the results from the two machines. Results for each time point from each analyzer were compared with all the other time points from both machines. Figure 3A shows the key to the cross correlations in Fig. 4B, C, and D for absolute CD4 counts, total lymphocyte counts, and percentages of CD4 lymphocytes, respectively.

FIG. 5.

Carry-over analyses for the Partec Cyflow SL_3 (a) and the FACSCalibur/Sysmex XT1800i dual-platform system (b). These analyses assessed the effects of residual samples on subsequent runs.