Association of Stress Renography-Derived Renal Functional Reserve With Transplant Outcomes in Recipients of Kidneys From Living Donors With a Suboptimal Glomerular Filtration Rate

BACKGROUND: Living donor kidney transplantation remains a cornerstone of therapy for end-stage renal disease (ESRD), yet accurately characterizing the functional capacity of donors with suboptimal glomerular filtration rate (GFR) is difficult. Conventional renal function indices are static and do not capture the kidney's adaptive capacity. Renal functional reserve (RFR), a dynamic parameter derived from stress renography, may provide additional information for donor evaluation and prediction of transplant outcomes. METHODOLOGY: In this prospective observational study, 120 living donor-recipient pairs were evaluated. Donors with a pre-donation estimated GFR (eGFR) of 60-89 mL/min/1.73 m² underwent conventional renal assessment and stress renography to determine RFR. Recipient renal function and transplant outcomes were followed for 12 months. Multivariable linear regression, receiver operating characteristic (ROC) curve analysis, and Kaplan-Meier survival analysis were used to evaluate associations between RFR and transplant outcomes. RESULTS: Stress renography demonstrated an increase in GFR from 74.6 ± 8.1 to 89.8 ± 10.4 mL/min/1.73 m², yielding a mean RFR of 15.2 ± 4.3 mL/min/1.73 m². Higher donor RFR was associated with lower recipient serum creatinine during the early postoperative period and higher recipient eGFR during follow-up. In multivariable linear regression, RFR was independently associated with recipient eGFR at 12 months (standardized β = 0.487, p < 0.001; model R² = 0.45). RFR demonstrated a higher AUC for delayed graft function than baseline eGFR and serum creatinine; the difference between RFR and baseline eGFR was statistically significant by the DeLong test (p = 0.014). CONCLUSIONS: Stress renography-derived RFR was independently associated with recipient renal function beyond conventional renal function assessment in living kidney donors with suboptimal baseline eGFR. Higher RFR was associated with better recipient eGFR at 12 months and demonstrated greater discrimination of delayed graft function than baseline eGFR. Larger multicenter studies with longer follow-up are required to validate these findings before routine clinical implementation.