Absolute and percent CD4+ T-cell enumeration by flow cytometry using capillary blood

CD4+ T-cell counting is usually performed on whole blood obtained from standard venipuncture. Venipuncture requires expertise, results in discomfort and generates biological waste. Capillary blood could be used to measure the levels of CD4+ T-cell in children, elderly and very ill patients. We studied the agreement between CD4+ T-cell counts and percent generated using venous blood with those obtained with capillary blood in HIV-infected adults and children in a resource-limited tropical setting.

This cross-sectional study consecutively enrolled a total of 152 adult and pediatric HIV-positive patients attending two outpatient clinics in Maputo City, Mozambique. We recruited individuals presenting for their routine clinical follow-up that included the determination of CD4+ T-cell counts in peripheral blood. For each subject, peripheral blood specimens were obtained by both venipuncture and finger prick. Specimens were tested using two flow cytometers, the FACSCount and the FACSCalibur.

Absolute CD4+ T-cell counts obtained using capillary blood were in close agreement with those from venous blood both on the FACSCalibur (absolute bias=+12.3 cells/mm³, limits of agreement: -259.2 to +283.9, R²=0.96) and the FACSCount (absolute bias=+16.1 cells/mm³, limits of agreement: -209.2 to +241.5, R²=0.97). Percent CD4+ T-cell counts were measured only on the FACSCalibur also showed a good agreement with a bias of +0.6% and limits of agreement of -3.1 to +4.3.

Absolute CD4+ T-cell counts and percent generated using capillary blood are in close agreement with those from venous blood. Point-Of-Care assays and standard flow cytometers can be deployed in a tiered laboratory network where both venous and capillary blood collection can be used for CD4+ T-cell enumeration.