Background : Advances in immunosuppression after kidney transplantation have decreased the influence of early acute rejection (EAR) on graft survival. Several studies have suggested that late acute rejection (LAR) has a worse impact on long-term graft survival than EAR. We investigated whether the timing of acute rejection influences graft survival and analyzed risk factors for EAR and LAR.

Methods : We performed a retrospective cohort study involving 706 patients who underwent kidney transplantation between 2000 and 2009 at the Samsung Medical Center. Follow-up lasted until June 2011. Recipients aged less than 18 years, patients with multiple organ transplants, repeated kidney transplantation, primary non-functioning transplants, follow up loss and death with a functioning graft and patients who had both EAR and LAR were excluded. Patients were divided into 3 groups: no AR, EAR and LAR. EAR and LAR were defined as rejection before 3 months and after 3months, respectively. The characteristics of 3 groups were compared. Differences in graft survival between the 3 groups and risk factors of graft failure were analyzed. 1yr, 3yr, 5yr eGFR were compared between 3 groups. Logistic regression analysis was performed to determine predictive of EAR and LAR.

Result : Of the 706 patients, 194 patients (27.5%) had biopsy- proven AR. [EAR 96 patients (49%); LAR 98 patients (51%)]. There was no difference in recipients’ age, BMI, underlying DM, PRA, induction protocol, dialysis duration, cold ischemic time, delayed graft function, immunosuppression regimen and donor age between 3 groups. Patients with EAR were more likely to be male than the no AR (P <0.001) and LAR group (P=0.03). Proportion of living donors was higher in the EAR group than the no AR group (P< 0.001). Both EAR and LAR were more likely to be HLA mismatched than no AR group (P= 0.002). In time dependent cox regression analysis EAR (HR 2.67: 95% CI 1.18-6.08) and LAR (HR 5.36: 95% CI 2.64-10.9) were significantly related to graft failure. When we set the LAR as standard and compare it with EAR. There was no statistical difference between EAR and LAR (P = 0.15). GFR was lower in LAR group than the EAR group (P <0.001).

Conclusion : AR, regardless of its timing, significantly worsened graft survival. Treatments reducing the incidence of AR and improving prognosis are needed.