Technical and clinical aspects of the histocompatibility crossmatch assay in solid organ transplantation

The presence of antibodies directed against human leucocyte antigens (HLA) expressed on donor cells is a significant risk factor for serious clinical complications after transplantation. Therefore, the crossmatch assay is one of the most important tests available to the histocompatibility laboratory for the detection of donor-specific anti-HLA antibodies in potential allograft recipients. Early crossmatch methods utilized complement-dependent cytotoxicity, which is useful for detecting donor-specific anti-HLA antibodies responsible for hyperacute allograft rejection but lacks adequate sensitivity. Consequently, more sensitive crossmatch methods were developed ultimately leading to the flow cytometry crossmatch as the currently preferred methodology. We review herein the evolution of the crossmatch assay and the most important factors to consider while performing and interpreting the results of this fundamental assay for the long-term survival of the transplanted organ.