Comparison of different methodologies for CD4 estimation in a clinical setting.

OBJECTIVE

To compare flow cytometry assays, using traditional dual platform (DP) or newer single platform (SP) for CD4 enumeration.

METHOD: Records of subjects enrolled in four separate clinical trials using the same central laboratory [SP methodology (Trucount)] were reviewed retrospectively. Eighteen subjects had 60 matching contemporaneous samples at multiple timepoints.

RESULTS

DP flow cytometry yielded higher CD4 counts in 50/60 assays (83%). CD4 count and percentage by the two methods showed strong correlation for the counts (r=0.965, P<0.0001) and percentages (r=0.959, P<0.0001). Bland-Altman plot analysis showed that the limits of variation were within agreeable limits of +/-2SD in 56/60 (93.3%) samples tested. Twenty-five (42%) samples had a difference of >50 cells/microL. Of these six (24%) exceeded 100 cells.

CONCLUSION

This study is in agreement with previous reports of strong correlation between DP and SP flow cytometry. This review found differences in CD4 counts in a high proportion of samples tested highlighting the importance for clinicians to be aware of such differences when interpreting results from the two methods.