Introduction The measurement of CD4 count for HIV-infected individuals relies on flow cytometry methods. The standard one is a single platform technology, which uses 50 µl of samples and 10 µl of monoclonal antibodies. To reduce the CD4 count cost, we propose to asses a modified method based on reducing the sample and monoclonal antibodies volumes.

Methods Between February and May 2011, we have tested 90 samples of HIV-infected persons by the standard method i.e using 50 µl of anticoagluated blood and 10 µl of monoclonal antibodies (CD3FITC/CD4PE/CD45PerCP, Becton-Dickinson) and by the modified method i.e using 20 µl of anticoagluated blood and 2 µl of monocolonal antibodies (CD3FITC/CD4PE/CD45PerCP, Becton-Dickinson), in our laboratory. The % of CD4 as well as the absolute count (TrueCount, Becton-Dickinson) was determined for both methods by using Cellquest-Pro on FacsCalibur (Becton-Dickinson). Linear regression and Bland and Altman analysis were performed to assess correlation and agreement between both methods.

Results When analysing the whole sample, the modified method showed a strong correlation with the standard method, r = 0.99 for CD4 count percent. Bland and Altman analysis revealed a mean bias of –0.1% (Limit of agreement: –3.0, 2.8). Regarding the absolute count of CD4, r was 0.99 and the mean bias was 9 cells/µl (LOA:-64.8, 82.5). When the statistical analysis is performed for the strata of CD4 ≤ 350, the r was 0.98, and the mean bias was –1 cell/µl (LOA: –44.1, 42.2).

Conclusion The modified method based on reducing blood and antibodies volumes showed similar results to the standard method. This low cost method may be an interesting alternative method to measure CD4 count in developing countries.