Donor-Recipient Size Mismatch is a Critical Determinant of Kidney Transplant Outcome

In kidney transplantation, the donor kidney should provide sufficient nephron mass to meet recipient demands. Although nephron mass cannot be easily measured, size-mismatch metrics could be useful surrogates for nephron supply and requirement. However, the impact of donor-recipient size-mismatch on post-transplant-kidney outcome remains uncertain.

Population cohort study using United Network for Organ Sharing data (2010-2024) including adult kidney-only transplants. Multivariable nonlinear (restricted cubic spline) regression models with interaction terms were used to analyze associations. Primary size-mismatch metric was donor-recipient body-surface-area (BSA) ratio, because BSA is a well-established surrogate for nephron number and requirement.

In 155,438 single-kidney transplants, donor-recipient BSA-ratio was associated with 1-year estimated glomerular filtration rate (eGFR), 1- and 5-year graft survival (all P < 0.001), with small donor kidneys in larger recipients having consistently inferior outcome. Keeping other factors constant, BSA-ratio in the 5th percentile versus 95th percentile (0.76 vs. 1.37) was associated with a 1-year eGFR of 50.7 versus 71.2 ml/min per 1.73 m² (difference = 20.5, 95% confidence interval [CI] = 19.9-21.1) and the hazard of 5-year graft loss was almost doubled (adjusted hazard ratio [aHR] = 1.93, 95% CI = 1.75-2.13). After donor age, donor-recipient BSA-ratio was most strongly associated with 1-year eGFR, with a stronger association than the other 34 examined factors. Nonlinear interaction analyses revealed the association between BSA-ratio and outcome remained consistent regardless of donor age or donor-recipient sex-mismatch.

Donor-recipient size-mismatch, measured by BSA-ratio, is strongly associated with post-transplant outcome. It is more strongly associated with outcome than most other factors used in current offering schemes and risk indices. Therefore, size-mismatch should be considered in kidney offering schemes and adjusted for as a critical potential covariate and/or confounder in observational studies and prospective trials.