The role of positive flow cytometry crossmatch in late renal allograft loss.

Many studies relating flow cytometery crossmatch (FCXM) results to kidney transplant outcomes have examined risk in the first 3 to 12 months. We used Organ Procurement and Transplant Network registry data for 66,594 kidney transplants from 1995 to 2007 to investigate associations of T-cell positive (T+) and T-cell negative/B-cell positive (T(-)B+) FCXM with graft failure risk early (years 0-1) and late (years >1-5) after transplant. Compared with transplants with T-cell negative/B-cell negative (T(-)B(-)) FCXM, living-donor transplants performed after T+ FCXM had significantly higher adjusted, relative risks of both early (adjusted hazards ratio [aHR] 1.71, p < 0.0001) and late (aHR 1.36, p = 0.017) graft loss. T(-)B+ FCXM was associated with approximately 40% higher relative risk of graft loss in the late period only. Patterns were similar for deceased-donor transplants. The risks of positive FCXM persist beyond the peritransplant period for years after transplant. Damage by memory effector cells may explain the long-term risks associated with positive FCXM.