Transplantation with positive complement-dependent microcytotoxicity crossmatch in contemporary kidney transplantation: Practice patterns and associated outcomes.

We analyzed clinical factors and graft survival associated with complement-dependent microcytotoxicity (CDC) crossmatch (XM) positive (+) kidney transplants in 1995 to 2009 United Network of Sharing (UNOS) registry data. CDCXM negative (-) transplants were selected from centers and years in which at least one CDCXM+ transplant was performed at a given center in a given year. CDCXM+ and CDCXM- results were compared with bivariate and multivariate survival analysis. Our observations are as follows: (1) The risk of graft loss with CDCXM+ vs. CDCXM- results was markedly lower than the risk observed historically, e.g., living donor (LD)-CDCXM+ absolute all-cause graft survival reductions were 0.7% at 24 hours (P=0.007), 2.9% at one year (P <0.0001), 3.7% at five years (P<0.0001); deceased donor (DD)-CDCXM+ absolute graft survival reductions were 0.7% at 24 hours (P=0.02), 3.5% at one year (P <0.0001), 2.7% at five years (P=0.0009). On covariate adjustment, the only significant association of CDCXM+ vs. CDCXM- results was with one-year graft loss risk: LD aHR 1.44 (95% CI 1.05-1.96), DD aHR 1.33 (CI 1.10-1.61). (2) CDCXM+ transplantation was more commonly performed among groups disadvantaged with respect to transplant access, including sensitized, previously transplanted women and black recipients. (3) In CDCXM+ recipients, there was a high percentage of flow cytometry (FC) XM- and autoXM+ results. After removing these groups, outcomes with CDCXM+ results were relatively good. (4) CDCXM+/FCXM+ vs. CDCXM-/FCXM- graft loss risk was observed only in LD recipients transplanted at centers performing fewer than 10 such transplants during the study period: 11.0% reduction (P<0.0001) and aHR of 2.86 (CI 1.18-6.94) at one year; 14.7% reduction (P<0.0001) and aHR of 1.77 (CI 0.88-3.58) at five years. Although using CDCXM+ as a contraindication to transplantation has been associated with virtual elimination of hyperacute rejection, the negative effect of a CDCXM+ in contemporary practice is relatively small, questioning the value of the CDCXM as a standalone test.