CD4 Lymphocyte enumeration: comparison between flow cytometry and enzyme immunoassay

Assessment of the CD4 lymphocyte number, currently performed by flow cytometry, is one of the main laboratory tests for establishing progression to acquired immunodeficiency syndrome (AIDS). An enzyme immunoassay has recently been commercialized which can be very useful for counting CD4 cells in laboratories where flow cytometers are not available. In the present study, a comparative evaluation of CD4 positive lymphocytes with flow cytometry and the enzyme assay was made in healthy subjects (N = 30, R = 0.88, P < 0.0001), human immunodeficiency virus (HIV)-infected individuals (N = 80, R = 0.91, P < 0.0001), and patients with autoimmune diseases (N = 28, R = 0.82, P < 0.001) or psoriasis (N = 18, R = 0.76, P = 0.01). A correlation between the two methodologies was not found in psoriatic patients under treatment with cyclosporin A (N = 7, R = 0.05, not significant). Some differences could be found at low CD4 lymphocyte levels since the influence of CD4 antigen eluted from monocytes or soluble CD4 in the whole blood sample could cause overestimation of CD4 cell numbers by the enzyme assay.