Evaluation of T cell subsets by an immunocytochemical method compared to flow cytometry in four countries.

The authors tested an alternative method for CD4 and CD8 T lymphocytes enumeration, the immunoalkaline phosphatase method (IA), in three African countries and in Denmark. The IA determinations from 136 HIV antibody positive and 105 HIV antibody negative individuals were compared to the corresponding results obtained by flow cytometry (FC) performed in the respective countries. The authors found good correspondence between the two methods for measurements of CD4 and CD8 T lymphocytes independent of serological status and geographical site. However, the CD4 and CD8 T lymphocytes values obtained by the two methods are not interchangeable as IA compared to FC consistently gives higher percentage of CD4 T lymphocytes, and lower percentage of CD8 T lymphocytes. Mean differences between the two methods did not differ between the three African countries indicating that the IA method provides systematic results. Replicate measurements suggested good correspondence between results obtained by IA. By using an IA level of < 300 CD4 T lymphocytes/microliter, the sensitivity was 81% and specificity 96% for detecting an FC level of < 200 CD4 T lymphocytes/microliter. Using an IA level of < 20% CD4 T lymphocytes, the sensitivity was 89% and specificity 95% for detecting an FC level of < 14% CD4 T lymphocytes. The FC and IA methods had the same internal correspondence between low absolute CD4 T cell count and low CD4 percentages; the sensitivity and specificity for detecting a low absolute CD4 T cell counts with a low CD4 percentage was 92% and 68% for FC and 91% and 73% for IA, respectively. The IA method is 10-fold cheaper than FC, is independent of advanced laboratory facilities, and does not need immediate processing of samples as blood smears can be stored for long periods. The IA method is therefore suitable for use in areas with limited resources and laboratory facilities where there is a need for immunological surveillance in hospital or community studies.