Strong False-Positive Pretransplant Flow Cytometric Crossmatch Induced by Non-HLA Autoantibodies in a Nonsensitized Renal Transplant Candidate.

Flow cytometric crossmatch (FCXM) is a sensitive method for detecting donor-specific antibodies in kidney transplantation; however, false-positive results may occur in the absence of HLA antibodies. We report a case of a 46-year-old nonsensitized male kidney transplant candidate who demonstrated persistent strong T-cell FCXM positivity despite repeatedly negative HLA antibody screening by single antigen bead assay. Complement-dependent cytotoxicity crossmatch was negative for both T and B lymphocytes. The patient had no history of prior sensitizing events, including transfusion, transplantation, or pregnancy. To exclude assay interference, serum pretreatment with EDTA, serial dilution, heat inactivation, and dithiothreitol was performed, and no clinically relevant HLA donor-specific antibodies were identified. Extended non-HLA antibody screening revealed multiple autoantibodies, including antibodies against viemtin, leucine-rich repeat transmembrane protein 2, tubulin alpha-1B chain, and CD36. These non-HLA autoantibodies were considered the most likely cause of the isolated T-cell FCXM positivity. This case highlights the diagnostic challenge posed by discordant crossmatch results and emphasizes the importance of considering non-HLA antibodies in the interpretation of FCXM. Identification of non-HLA antibody-mediated FCXM positivity may help avoid unnecessary exclusion of transplant candidates and support more informed immunologic risk assessment in pretransplant evaluation.