Evaluation of Pretransplant Donor-Specific Alloantibodies With Different Crossmatch Techniques

Donor-recipient crossmatching for kidney transplantation is an obligatory step for the transplant work-up process. Attention is currently put on single bead assay (SBA) that enables virtual crossmatching. In contrast, methods developed for complement binding capacity are still not routinely established. We compared modified, cytolytic flow cytometry crossmatch (cFC-XM) with complement-dependent serological crossmatch (CDC-XM), SBA, and flow cytometry crossmatch (FC-XM) to verify whether newly developed techniques may be beneficial for transplant immunological matching. Also, the cutoff value for donor-specific alloantibodies levels currently used for virtual crossmatch was verified. Serum from 22 sensitized patients was crossmatched with surrogate donors by CDC-XM, FC-XM, and cFC-XM, while anti-HLA antibodies were measured by SBA. In all cases, virtual crossmatch was positive at 5000 mean fluorescence intensity cutoff. Among 22 tested sera with donor-specific alloantibodies above 5000 mean fluorescence intensity, the positive CDC-XM result was noted only in 41% of patients (n = 9), but positive FC-XM was noted in 86% (n = 19), and further lytic antibodies (cFC-XM) were confirmed in 27% of cases (n = 6). Our results suggest that donor-recipient immunological matching for kidney transplantation requires different methods to verify the importance of alloantibodies, and improvement in laboratory investigation is needed. This is especially important for immunized patients that have many types of alloantibodies and virtual crossmatching used as a tool for deceased donor allocation should balance between the likelihood of transplantation and risk of positive crossmatch result.