Evaluation and short-term impact of functional renal reserve in extended criteria vs. healthy donors

A single-center observational study.

Abstract

Introduction: In the face of the growing demand for organs, the use of donors with extended criteria requires precise methods to assess their post-nephrectomy safety. This study evaluates functional renal reserve (RFR) in healthy donors and in donors with extended criteria, comparing the oral protein load test with Doppler-derived variation in the intraparenchymal renal resistance index (VIRRI). We analyze whether VIRRI, a non-invasive technique based on vascular autoregulation under abdominal pressure, can replace complex methods for predicting renal compensatory capacity.

Materials and methods: An observational and prospective study was conducted in two transplant centers with 32 adult donors (eGFR >80 ml/min/1.73 m²). Functional renal reserve (RFR) was compared using two methods: oral protein loading (1.2 g/kg) with creatinine clearance, and the intraparenchymal renal resistive index (VIRRI) variation test by Doppler ultrasound under abdominal mechanical stress. Statistical analysis included Student's t-tests, Pearson correlation and Mann-Whitney U, considering significance with p < 0.05 and 95% confidence intervals.

Results: We included 32 participants (27 with extended criteria; 5 healthy). Donors with extended criteria had higher age, weight, BMI, glucose, and LDL (P < 0.05). Although baseline eGFR was similar between groups (109 mL/min), functional renal reserve was significantly lower in the extended criteria group (39.3 ± 33.7 vs. 87.2 ± 71 mL/min; P < 0.05). No statistically significant correlation was found between the protein load measurement and the VIRRI test (R2 = 0.054).

Conclusions: Donors with extended criteria have a significantly lower RRF despite a normal baseline eGFR. Aging and metabolic alterations erode renal compensatory capacity, a phenomenon that conventional static assessments fail to detect. The lack of correlation among the evaluated methods underscores the need for dynamic protocols. Integrating RRF into donor selection optimizes risk stratification, thereby ensuring greater graft viability and longevity in kidney transplantation.