Evaluation of Dynabeads and Cytospheres compared with flow cytometry to enumerate CD4+ T cells in HIV-infected Ugandans on antiretroviral therapy.

BACKGROUND

Laboratory-based monitoring of antiretroviral therapy is essential but adds a significant cost to HIV care. The World Health Organization 2006 guidelines support the use of CD4 lymphocyte count (CD4) to define treatment failure in resource-limited settings.

METHODS

We compared CD4 obtained on replicate samples from 497 HIV-positive Ugandans (before and during ART) followed for 18 months by 2 manual bead-based assays, Dynabeads (Dynal Biotech), and Cytospheres (Beckman Coulter) with those generated by flow cytometry at the Infectious Diseases Institute in Kampala, Uganda.

RESULTS

We tested 1671 samples (123 before ART) with Dynabeads and 1444 samples (91 before ART) with Cytospheres. Mean CD4 was 231 cells/mm (SD, 139) and 239 cells/mm (SD, 140) by Dynabeads and flow cytometry, respectively. Mean CD4 was 186 cells/mm (SD, 101) and 242 cells/mm (SD, 136) by Cytospheres and flow cytometry, respectively. The mean difference in CD4 count by flow cytometry versus Dynabeads were 8.8 cells/mm (SD, 76.0) and versus Cytospheres were 56.8 cells/mm (SD, 85.8). The limits of agreement were -140.9 to 158.4 cells/mm for Dynabeads and -112.2 to 225.8 cells/mm for Cytospheres. Linear regression analysis showed higher correlation between flow cytometry and Dynabeads (r=0.85, r=0.73, slope=0.85, intercept=28) compared with the correlation between flow cytometry and Cytospheres (r=0.78, r=0.60, slope=0.58, intercept=45). Area under the receiver operating characteristics curve to predict CD4<200 cells/mm was 0.928 for Dynabeads and 0.886 for Cytospheres.

CONCLUSION

Although Dynabeads and Cytospheres both underestimated CD4 lymphocyte count compared with flow cytometry, in resource-limited settings with low daily throughput, manual bead-based assays may provide a less expensive alternative to flow cytometry.