Crossmatch Positivity: The Khalid Khwaja Memorial Chapter

Crossmatch techniques have evolved over time from (cell-based) complement-dependent cytotoxicity to flow cytometry tests and, more recently, to virtual crossmatches. Since about 40% of all pancreas grafts in the United States are “imported” from a different UNOS region, virtual crossmatches have a clear advantage over cell-based crossmaches by lowering cold ischemia times and delayed graft function rates, both of which result in improved outcome. The role of virtual crossmatches may further increase in the future even for highly sensitized patients as the correlation between cell-based and virtual crossmatches continues to improve. Pancreas transplants across immunologic barriers are rare and, in the past, were frequently the result of pretransplant crossmatch omission due to long ischemia times. Although no definitive assumptions about crossmatch positive pancreas transplants can be made due to overall relatively small numbers, the following conclusions can be drawn: (1) crossmatch positivity does not independently affect pancreas graft outcome, regardless of whether the crossmatch is T- or B-cell, current or historic; (2) hyperacute rejection is extremely rare in contrast to antibody-mediated rejection; (3) standardized desensitization protocols need to be developed for pancreas transplants; and (4) for the rare living donor pancreas transplant in the setting of a positive crossmatch, successful outcome can be expected using pretransplant desensitization protocols similar to those used in kidney transplantation.