Time-Varying Covariates and Risk Factors for Graft Loss in Kidney Transplantation

Objectives. The present study was designed to evaluate the factors involved in long-term graft survival in recipients of kidney transplantation. Materials and Methods. We reviewed 755 Iranian adult recipients who underwent kidney transplantation at Shahid Labbafinejad Medical Center in Tehran, Iran. Patients were followed for 5 years after transplantation. The primary outcome was the time between transplantation and graft loss. Using Cox regression, we studied the effect of time -independent variables (recipients' age and sex, donors' age, and type of donor), time -dependent covariates (body mass index [BMI], systolic blood pressure, diastolic blood pressure, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol levels, proteinuria and serum creatinine level), and immunosuppressive drugs on graft loss 60 months after transplantation. The results are presented as the hazard ratio (HR) with 95% confidence intervals. Results. Result from Cox proportional hazards model showed that the HR of graft loss was 1.62 (95% CI: 1.03-2.54) in cadaveric donor compared with living donor kidney recipients. The HR of graft loss for recipient age was 1.02 (95% CI: 1.002-1.030). Moreover, according to obtained results, the risk of losing functional transplant increased for each mg/dL rise in serum creatinine at least 9% and at most 40%. Our results also showed that 1 unit increase of BMI has at least a 2% and at most a 15% decremented effect on the hazard ratio of graft loss. Conclusions. Having lower levels of creatinine and receiving a kidney from a younger living donor were associated with a decreased risk of graft loss. Graft loss is more likely to occur in patients with lower BMI.