CELL-BASED ASSAYS: DETECTING HLA ANTIBODIES BEFORE SOLID-PHASE ASSAYS
Panel-reactive antibody testing, in general, estimates the percentage of potential donors to whom a recipient has HLA antibodies and approximates the risks of positive crossmatch. Early panel-reactive antibody assays used panels of 25-60 real donor cells selected to represent the common HLA phenotype distribution of the potential deceased donor population, which were then tested for complement dependent cytotoxicity with recipients sera. Results were subject to change with different donor cells in the panel, were less sensitive for rare HLA antigens, and detected only higher titer antibodies. Although still used in conjunction with other assays, cell panels are no longer used in isolation for panel-reactive antibody determination. The donor specific complement-dependent cytotoxicity crossmatch assays detects high-titer donor-specific HLA antibodies required to bind complement for demonstration of antibody presence, whereas lower titer donor-specific HLA antibodies may be detected by flow cytometry cross-matching, with a positive result requiring only antibody binding and not complement activation.