Donor‐Recipient Size Mismatch by Body Surface Area and Risk of Graft Failure in Kidney Transplantation

BACKGROUND: Donor-recipient size mismatch may contribute to long-term kidney allograft dysfunction through imbalances in nephron supply and recipient metabolic demand. Body surface area (BSA) integrates height and weight into a single physiologic measure and may offer a more precise index of size proportionality than conventional anthropometric data. METHODS: We analyzed 38,545 adult deceased donor kidney-only transplants performed in the United States between 2010 and 2015 using national registry data with complete 10-year follow-up. Donor and recipient BSA were calculated using the Mosteller formula, and the donor-to-recipient BSA ratio was modeled as both a continuous and categorical variable (<0.9 undersized, 0.9-1.1 matched, >1.1 oversized). Multivariable Cox and logistic regression models evaluated associations with death-censored graft failure (DCGF), all-cause graft failure (ACGF), patient mortality, and delayed graft function (DGF), adjusted for donor, recipient, and transplant factors. RESULTS: Undersized grafts (BSA ratio <0.9) were associated with higher risk of DCGF (HR 1.11, 95% CI 1.07-1.15), ACGF (HR 1.10, 1.06-1.14), and mortality (HR 1.07, 1.03-1.12), and DGF (OR 1.09, 1.03-1.16; all p < 0.01) compared with matched grafts. Oversized grafts showed no significant differences. Risk increased stepwise at stricter undersized thresholds (HR 1.13 at <0.85 and 1.17 at <0.8), indicating a dose-dependent relationship. CONCLUSIONS: BSA mismatch, specifically under sizing, was independently associated with worse graft and patient outcomes. The BSA ratio adds prognostic value beyond standard variables and may improve allocation by accounting for nephron adequacy.