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Time-dependent risk factors influencing the long-term outcome in living renal allografts: donor age is a crucial risk factor for long-term graft survival more than 5 years after transplantation.

BACKGROUND
Most investigations have revealed that the improvement in early graft survival has not resulted in a corresponding improvement in long-term graft survival. The risk factors for long-term graft survival should be clarified.


METHODS
A single-center experience of 1100 consecutive renal transplant recipients who received kidneys from living donors from 1983 to 1998 was reviewed to clarify the time dependency of risk factors for long-term graft survival. We examined various possible risk factors, including HLA-AB and -DR mismatches, ABO-blood group incompatibility, graft weight, donor age and sex, recipient age and sex, and the presence or absence of acute rejection by using the time-dependent, nonproportional Cox's hazards model.


RESULTS
Acute rejection episode, donor age, HLA-AB 4-antigen mismatches, ABO-incompatible transplantation, smaller kidney weight compared with the patient's body weight (Kw/Bw ratio less than 2.67), and transplantation from an unrelated living donor were risk factors for long-term graft outcome. Multivariate analysis for time-dependent risk factors showed that donor age of more than 60 years was the most important risk factor for long-term graft failure after 5 years posttransplantation (hazard ratio: 2.57). In contrast, acute rejection, ABO incompatibility, and nonrelated donors were significant risk factors for short-term graft failure within 5 years after kidney transplantation (hazard ratios: 2.68, 1.57, and 1.69, respectively).


CONCLUSIONS
Donor age of more than 60 years was a crucial risk factor affecting long-term graft survival. In contrast, acute rejection, ABO incompatibility, and nonrelated donors were significant risk factors for short-term graft failure.