Small kidneys for large recipients: does size matter in renal transplantation?

Background: Imbalance between transplanted renal mass and the metabolic demands of the recipient has been identified as a predictor of renal graft function. Multiple factors have been used to test this influence, but none of them is consensually accepted. The aim of this study is to evaluate the influence of the imbalance between transplanted renal mass and the metabolic needs of the recipient by analyzing the relationship between the ratio of the weight of the renal graft and the body weight of the recipient (Kw/Rw) on transplantation outcomes.

Methods: Prospective observational study of 236 first and single cadaveric renal transplants in non-hyperimmunized recipients was conducted. Grafts were orthogonally measured and weighed immediately before implantation, and these measures were correlated with donor and recipient data. According to the Kw/Rw ratio, patients were divided into three groups: Kw/Rw < 2.8 (P25), Kw/Rw = 2.8-4.2, and Kw/Rw > 4.2 (P75). After a mean follow-up of 5.2 years, transplant outcomes (delayed graft function; acute rejections; and estimated 1-, 6-, 12-, 36-, and 60-month renal function, graft, and patient survivals) were evaluated and correlated in uni- and multivariate analyses with the Kw/Rw ratio.

Results: Mean values for graft dimensions were 109.47 × 61.77 × 40.07 mm and the mean weight was 234.63 g. Mean calculated volume was 145.64 mL. The mean Kw/Rw ratio was 3.65 g/kg. These values were significantly lower for female grafts (3.91 vs 3.24, P < .001). According to the Kw/Rw ratio groups, there were no differences on delayed graft function, acute rejection episodes, and estimated graft function at the defined times. The increase in estimated glomerular filtration rate by a mean of 3.6 mL/min between 1 and 6 months for patients with Kw/Rw < 2.8 was not statistically relevant when compared to the higher ratio group with a mean variation of -0.91 mL/min (P = .222). Graft survival rate at 5 years after transplantation was 79% in the Kw/Rw < 2.8 group and 82% in the Kw/Rw > 4.2 group (P = .538). Patient survival rate at 5 years after transplantation was 85% in the Kw/Rw < 2.8 group and 92% in the high ratio group (P = .381). Kw/Rw ratio was not an independent risk factor for transplant failure at 5.2 years in a multivariate logistic regression analysis. Irrespective of recipient weight, graft survival was significantly higher for grafts with volume or weight above the 50 percentile (vol > 134 mL, P = .011 or weight > 226 g, P = .016).

Conclusion: The imbalance between implanted renal mass and recipient metabolic demands does not seem to influence the functional outcomes and graft survival up to 60 months post-transplantation. Nevertheless, irrespective of recipient weight, graft survival is significantly higher for grafts with volume or weight above the 50 percentile.