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Field Testing of a Portable Microchip Assay For CD4 Counts in Botswana S. Graham1,2, W. Rodriguez1,2,3, N. Christodoulides4, D. Romanovicz4, M. Dixon3, A. Goodey4, T. Peter5, S. Zavahir5, I. Thior5, S. Lockman1,5,6, R. Shapiro5,6, M. Essex5,6, B. Walker2,3, J. McDevitt4 1Brigham & Women’s Hospital, 2Harvard Medical School, 3Partners AIDS Research Center, Boston, MA, USA; 4University of Texas, Austin, TX, USA; 5Botswana-Harvard Partnership, Gabarone, Botswana; 6Harvard School of Public Health, Boston, MA, USA Background: CD4 count monitoring is a critical element in the management of HIV-infected patients, but CD4 counts remain unavailable in many high-prevalence areas. A new microchip CD4 assay will soon be available to help alleviate this problem. The objective of this study was to compare the microchip assay with gold standard flow cytometry in a resource-poor setting. Methods: Whole blood was collected as part of the Mashi study, an ongoing study of maternal-child transmission in Botswana. Microchip specimens were analyzed on the day of collection. Thirty-three microliters of blood were obtained, and, following antibody staining and dilution, imaged under fluorescence. Images were analyzed using an automated counting algorithm for CD4 cells, CD8 cells, and total CD3+ lymphocytes. Microchip CD4 and CD8 percentages were correlated with flow cytometry data. Results: Preliminary data on the first 23 samples analyzed show a strong correlation between microchip-based CD4 percent and CD4 percent obtained by flow cytometry (R2=0.879), with closer correlation among samples with absolute CD4 counts &Mac178;200 cells/mm3 (R2=0.973). Correlation for CD8 percent was less close (R2=0.747), possibly reflecting differences in antibody quality. Further data are accruing. Conclusions: The CD4 microchip is a low-cost, portable alternative to flow cytometry that provides accurate results across a wide range of CD4 percentages. For resource-poor settings in which cost, transportation, or technical problems preclude access to flow cytometry, the microchip has great potential to improve HIV care. |