Comparison Of Different Methodologies For Cd4 Estimation In A Clinical Setting

ObjectiveTo compare flow cytometry assays, using traditional dual platform (DP) or newer single platform (SP) for CD4 enumeration.MethodRecords 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.ResultsDP 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/mu L. Of these six (24%) exceeded 100 cells.ConclusionThis 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.