Evaluation of alternative CD4 technologies for the enumeration of CD4 lymphocytes

Enumeration of CD4+ T cells from persons infected with the human immunodeficiency virus (HIV) is important. Traditionally this measurement has been calculated by multiplying the percent of lymphocytes that are CD4+ T cells (from flow cytometry) and the number of lymphocytes per microliter of blood (from hematology measures). Recently, several manufacturers have developed new techniques for determining absolute numbers of CD4+ and CD8+ cells without the need for the flow cytometer and hematology analyzer. We evaluated these methods for accuracy (comparison with traditional methodology) and precision (variability of replicate determinations) as well as for use with specimens older than 1 day. Precision of the assays as determined by the coefficients of variation (CV) from replicates varied from about 3% to about 12%, depending on the assay and the HIV status of the patient. Correlation coefficients of test method results with the standard methodology (r) were all greater than 0.9, and in most cases slopes were close to 1.0 for both CD4 and CD8. Though each methodology will meet different requirements in the laboratory, our results indicate that these assays are all acceptable for enumerating CD4 and CD8 cells in HIV+ as well as HIV- patients.