Reduction of variation in T-cell subset enumeration among 55 laboratories using single-platform, three or four-color flow cytometry based on CD45 and SSC-based gating of lymphocytes

Background: Enumeration of CD4(+) and CD8(+) T-cell subsets provides relevant information for diagnosis and monitoring of patients with cellular immunodeficiencies. As a result, an external quality assurance scheme was implemented in Belgium, The Netherlands, and Luxemburg in 1995. A workshop was held to train the participants in state-of-the art technology for assessment of absolute T-cell subset counts (i.e., a three or four-color, single-platform assay with lymphocyte gating based on CD45 and sideward light scatter) with the aim to achieve between-site coefficients of variation (CVs) <10% and within-site Us <5% for greater than or equal to75% of the participants. Methods: Three send-outs of stabilized blood from a healthy donor were distributed to 55 laboratories, each with the request to perform the standard assay on three occasions. For comparison, each laboratory performed its local technique in parallel. Results: With the standard technique, between-site Us of similar to8% (CD3(+) T cells), similar to9% (CD4(+) T cells), and similar to10% (CD8(+) T cells) were achieved. Within-site CVs were <5% for 82% (CD3(+) T cells) and similar to70% (CD4+ and CD8+ subsets) of the participants. Local techniques yielded between-site CVs of 13%-17% for CD3+, CD4+, and CD8+ T cells. Conclusions: The state-of-the-art technology for T-cell subset enumeration was implemented successfully among 55 Belgian-Dutch laboratories and resulted in significant reductions of between-site variation of absolute CD3+, CD4(+), and CD8(+) T-cell counts. Cytometry (Clin. Cytometry) 50:92-101, 2002. (C) 2002 Wiley-Liss, Inc.