The One Lambda™ FlowDSA-XM™ assay is a flow cytometry–based crossmatch assay optimized for the detection of leukocyte antibodies. Combining traditional flow cytometry cellular crossmatch testing with the specificity of microbeads technology, the FlowDSA-XM assay selectively distinguishes leukocyte antibodies from autoantibodies. After incubating lymphocytes with human serum, any bound IgG on the cell surface is tagged with R-PE–labeled anti–human IgG. FlowDSA-XM Capture Beads bind selectively with the resulting antibody/antigen/anti–human IgG complex, and the fluorescent intensity is measured to indicate the relative amount of leukocyte antibody present in the serum.