Aim: The virtual crossmatch (VXM) is performed to assess HLA compatibility between recipient and prospective donors prior to transplant. Many organ offers are declined for HLA- or non-HLA related factors. With an aim of identifying ways to reduce refusal rates, particularly for HLA-related reasons, we sought to establish the transplant acceptance rates and categorize reasons for refusal.
Methods: VXMs performed in 2024 for deceased donor kidney were retrospectively reviewed. Donor specific antibody (DSA) status, recommendations to the transplant group, and whether the transplant occurred were noted. For cases where transplant did not occur, refusal reasons were categorized.
Results: In total, 1333 VXMs were performed for 485 candidates. Of these recipient:donor pairs (RDPs), 265 proceeded to transplant, resulting in a transplant-to-VXM ratio of 265/1333 (1:5). Low-level DSAs were reported for 37/265 RDPs in the transplanted group and 257/1068 in the non-transplanted group; RDPs without DSA were 1.9 times as likely to be transplanted (p < 0.001). Reasons for offer refusal were available for 546 of the 1068 RDPs (table 1). Most refusals (469/546; 85.9%) were non-HLA related. Only 14.1% (77/546) of refusals were related to a positive VXM and/or physical crossmatch (PXM). For 35/77 VXMs, transplant was not recommended due to high-level DSAs, 14 of which were allele-specific DSAs. For 42/77, the VXM recommended a prospective antibody testing and/or a prospective PXM on a recent sample given the presence of low-to-intermediate DSAs. Prospective PXM was only performed on 4 of these cases and were positive.
Conclusion: With a low transplant-to-VXM ratio of 1-in-5 and considering that only 14.1% of refusals were related to HLA, we wonder if VXM consults are overutilized in our institution. Regarding cases that were not recommended due to high-level DSA, VXMs could have been avoided if the unacceptable antigens had been updated in UNet and if high-resolution, deceased-donor typing was routine practice, which would help exclude organs with unacceptable allele-specific types. Further, the recommendation of additional testing on the VXM appears to be a deterrent for pursing organ offer. Future directions include a collaboration with the transplant group to better understand their screening process and identify possible areas of improvement to facilitate effective use of the VXM.
