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.