The Clinical Importance of Flow Cytometry Crossmatch in the Context of CDC Crossmatch Results

BackgroundThe complement-dependent microcytotoxicity crossmatch (CDCXM) is a standard method for evaluating the presence of preformed antibodies before transplantation. The flow cytometry crossmatch (FCXM) is more sensitive, but there is controversy regarding translation of its increased sensitivity to clinically relevant graft outcomes.MethodsWe analyzed Organ Procurement and Transplant Network registry data for living and deceased donor kidney transplants performed in 1995 to 2009 after both CDCXM and FCXM testing. Transplants with negative CDCXM (CDCXM−) and with T-cell positive (T+), T-cell negative/B-cell positive (T−B+), or T- and B-cell negative (T−B−) FCXM results were included. Graft survival according to crossmatch results was compared by survival analysis.ResultsAmong patients transplanted with negative CDCXM (CDCXM−), deceased and living donor graft recipients with T+ FXCM experienced significant absolute reductions in 5-year graft survival of 11.5% and 8.8% compared to those with T− FCXM (P < .0001). Compared to patients with FCXM−/CDCXM− deceased and living donor recipients with T−B+ FCXM/CDCXM− had absolute reductions in 5-year graft survival of 9.6% and 7.6%, respectively (P < .0001). Upon multivariate adjustment with Cox regression, T+ FCXM/CDCXM− deceased donor transplantation was associated with 51% higher adjusted relative risk of 1-year graft loss than FCXM−/CDCXM−. Relative risks were more marked at 1 year for the T+ groups but stronger in the 1- to 5-year interval for the T−B+ groups.ConclusionPositive FCXM has important prognostic implications even when CDCXM is negative. Thus, positive FCXM should not routinely be dismissed as “overly sensitive” when CDCXM is negative.