Effects of body mass index at transplant on outcomes of kidney transplantation

Backgound. While obesity increases postoperative complications and cardiovascular risks, its effects on long-term kidney transplant outcomes are less clear. Methods. We used data from the Australian and New Zealand Dialysis and Transplant (ANZDATA) Registry to examine the relationships between body mass index (BMI, classified according to World Health Organization criteria) at transplant and transplant outcome. Patients starting renal replacement therapy from April 1991 and who received a single-organ, primary kidney transplant (when aged 16 years) from April 1991 to December 2004 were included, and followed up to death or December 2005. Survival outcomes adjusted for important covariates were analyzed using Cox models, and cause-specific failures by competing risks analysis. Analysis using BMI at various times posttransplant was also performed. Intermediate outcomes were delayed graft function (DGF) and any acute rejection at 6 months. Results. In all, 5684 patients were included. Obese patients had worse graft and patient survival only in univariate analyses, not in multivariate analyses (adjusted hazard ratio [HR] for graft loss: 1. 10 [0.94 -1.259], P= 0.25; for patient death: 1.02 [0.83-1.25], P=0.87). Underweight patients had greater late ( !5 years) death-censored graft loss (adjusted HR: 1.70 [1.10-2.641, P=0.02), mainly due to chronic allograft nephropathy. Obesity was associated with greater odds for DGF (adjusted OR: 1.56 [1.23-1.97], P < 0.001) and 6-month risk of acute rejection (adjusted OR: 1.25 [1.01-1.54], P=0.04). Conclusions. Obesity per se was not associated with poorer kidney transplant outcomes, although it was associated with factors that led to poorer graft and patient survival. Underweight was associated with late graft failure, mainly due to chronic allograft nephropathy.