The Influence of Donor to Recipient Size Matching on Kidney Transplant Outcomes

Background. Nephron endowment in renal transplantation is infrequently considered, but may have important implications for post kidney transplantation outcomes. In this population-cohort study, we analyzed the deceased-donor kidney transplant outcomes stratified by donor-to-recipient size ratios. Methods. Data for all deceased-donor adult kidney transplantation recipients between 2003 and 2015 were extracted from the UK Transplant Registry. We used weight as a surrogate marker for kidney size and defined the following mismatch categories (donor weight/recipient weight × 100): less than 75% (small donor kidney), 75% to 125% (weight matched kidney), and greater than 125% (large donor kidney). Univariable and multivariable analyses were undertaken to assess the relationship between this marker and patient outcomes. Results. Outcomes for 11 720 transplants were analyzed with weight mismatch stratified as follows; small donor kidney (n = 1608, 13.7%), weight matched kidney (n = 7247, 61.8%) and large donor kidney (n = 2865, 24.4%). On multivariable analysis, no significant differences were detected in overall (P = 0.876) or death-censored (P = 0.173) graft survival, or in rates of delayed graft function (P = 0.396) between these 3 groups. However, 12-month creatinine levels were found to decline progressively across the groups (P < 0.001), with adjusted averages of 144.2 μmol/L for recipients of small donor kidneys, 134.7 μmol/L in weight matched kidneys, and 124.9 μmol/L in recipients of large donor kidneys. In addition, patient survival was found to be significantly shorter in recipients of larger kidneys than those with weight matched kidneys (hazard ratio, 1.21; 95% confidence interval, 1.05-1.40; P = 0.009), which is inconsistent with the existing literature. Conclusions. Our data demonstrate that 12-month creatinine is influenced by donor-to-recipient difference in body weight, but that no such difference is observed for either delayed graft function or death-censored graft survival. However, we observed increased mortality in recipients receiving larger kidneys; an observation which conflicts with the existing literature and warrants further investigation