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LIMITATIONS TO ANTIBODY DETECTION USING SINGLE ANTIGEN FLOW BEADS.
Thomas M. Ellis, PhD , Howard M. Gebel, PhD , Karen L. Pierce, CHS and Robert A. Bray, PhD . Milwaukee WI, Blood Center of Southeastern Wisconsin, 53201, Histocompatibility and Immunogenetics Laboratory and Atlanta GA, Emory University Hospital, 30322, Pathology .
HLA antigen-coated beads are used for the detection/identification of HLA antibodies in multiple situations. Bead assays provide valuable information for the accurate interpretation of crossmatches for solid organ transplantation, platelet transfusion support and screening of blood products in cases of transfusion-related acute lung injury. Despite their increased use, little information is available addressing the fine specificity of beads coated with single HLA antigens (FlowPRA HD beads). We evaluated the reactivity of HD beads with sera previously documented to contain no HLA antibodies as assessed with FlowPRA screening and specificity beads. Four pools (seven sera each from 28 PRA negative subjects) and six sera from non-transfused male donors were each tested with HD beads. We observed 3/4 serum pools displayed positive reactivity with one or more of the individual HD beads, as did 5/6 of the individual sera. Our data demonstrate a discrepancy between HD beads and FlowPRA screening/specificity beads. Specifically, depending on the test serum, one or more HD beads exhibit levels of reactivity that must be interpreted as an HLA specific antibody. Assuming the accuracy of the screening/specificity results, our data indicate that HD beads cannot be used as a “stand-alone” test to evaluate patient alloreactivity and that positive results must be cautiously interpreted when HD beads are used to confirm the presence of HLA antibodies in sera with equivocal screening/specificity bead results. Had HD beads alone been used, these HLA antibody negative samples would have been reported as positive. In patients, the clinical ramifications of these observations would be the incorrect assignment of unacceptable antigens and/or inappropriate deferral of potential organ, platelet, or blood donors.