*Purpose: The occurrence of acute antibody-mediated rejection (ABMR) was higher in flow cytometric crossmatch (FCXM)-positive patients despite desensitization, and complement binding ability of donor specific antibody (DSA) was important to predict ABMR. We herein investigated the correlations between 1) complement C3d-binding ability of preformed DSA and risk of ABMR, and 2) the efficacy of desensitization on C3d-fixing ability of DSA and risk of ABMR in the XM-positive patients.

*Methods: Twenty-one patients with preformed DSA-positive and XM-positive were included in this study. We retrospectively analyzed C3d-fixing ability of preformed DSA before desensitization and the influence of desensitization on C3d-fixing ability. Our desensitization protocol was Rituximab, plasmapheresis and high dose immunoglobulin from 30 days before transplantation.

*Results: Six patients had non-C3d-fixing DSA and 15 patients had C3d-fixing DSA. The presence of C3d-fixing DSA was significantly associated with re-transplantation (p=0.012). The presence of C3d-fixing DSA before desensitization was likely to be associated with the incidence of acute ABMR within 3 months post-transplantation (p=0.04) and chronic ABMR (p=0.03). However, the persistence of C3d-fixing DSA after desensitization was unlikely to be associated with ABMR (p=0.92).

*Conclusions: The presence of preformed C3d-fixing DSA caused significantly higher risk of ABMR in FCXM-positive patients. The measurement of C3d-fixing ability of DSA was recommended especially before desensitization to predict ABMR.

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