Recipient Minus Donor Body Mass Index Difference and One-Year Graft Function After Living-Donor Kidney Transplantation

Background: Recipient minus donor body mass index (BMI) difference is an anthropometric exposure whose anatomical validity is unproven. We evaluated its association with 1-year graft function after living-donor kidney transplantation. Methods: This retrospective cohort included all 249 adult living-donor kidney transplant recipients at one center during 2013–2024. Adjusted linear regression assessed 1-year estimated glomerular filtration rate (eGFR) among recipients alive with functioning grafts. The sensitivity, 6-month, longitudinal, ranked-composite, and clinical-event analyses were exploratory, without adjustment for multiple comparisons. Results: All 14 recipients without 1-year eGFR had experienced graft loss or death, leaving 235 for the primary analysis. The adjusted estimate was −0.55 mL/min/1.73 m2 per kg/m2 BMI difference (95% confidence interval [CI] −1.06 to −0.05; p = 0.033), equivalent to −2.77 (95% CI −5.31 to −0.23) per 5 kg/m2. Alternative BMI parameterizations showed similar fit. Exploratory eGFR estimates varied by visit and model specification. The unadjusted graft-loss/death hazard ratio was 0.88 per 5 kg/m2 (95% CI 0.55–1.42; 14 events). The full-cohort ranked-composite interval included zero. Conclusions: The adjusted eGFR association describes survivors with functioning grafts; complementary exploratory analyses do not change this conditional interpretation. Residual confounding remains possible. BMI difference does not quantify anatomical size mismatch, and these findings do not establish causality or donor-selection thresholds.