Use of dried whole blood spots to measure CD4+ lymphocyte counts in HIV-1-infected patients.

As antiretroviral drugs become widely available in developing countries, practical, field-friendly, and cheap methods of measuring CD4+ lymphocyte counts need to be developed. We tested use of whole blood spots dried on filter paper to measure CD4+ lymphocyte counts. We obtained blood from 42 HIV-1-infected patients from Zambia. We dried blood spots on filter paper and measured CD4+ lymphocyte counts with an established commercial enzyme immunoassay. We compared these measurements with those obtained from matched liquid whole-blood samples analysed with standard flow cytometry. Results of the filter-paper method accorded well with flow cytometry CD4 counts greater than 200 cells/microL (mean difference 13.6 [SD 52.4]). Dried whole blood stored on filter paper could be developed into a field-friendly alternative for CD4+ lymphocyte count measurements.