Renal functional reserve in living kidney donors

Factors associated with renal functional reserve (RFR)-presence or absence-are not completely clear and remain underinvestigated.

In this observational study, we evaluated the characteristics associated with the presence or absence of RFR in healthy subjects-living kidney donors-before donation. Renal function was assessed with measured glomerular filtration rate (GFR)-the clearance of iohexol-and RFR with the infusion of amino acids. An increase in GFR >10% after amino acid infusion indicated the presence of RFR. We defined a priori three groups of donors: without, with and using RFR. Subjects using RFR had a baseline GFR >100 ml/min but without an increase in GFR after stimulation.

Subjects without RFR were predominantly women (81%) with the lowest body surface area (BSA; 1.71 ± 0.17 m²) and basal GFR (85 ± 9 ml/min). Subjects with RFR were also mostly women (85%), with a higher BSA (1.83 ± 0.18 m²; P = .039) and basal GFR (93 ± 15 ml/min). Subjects using RFR were mostly males (56%) and had the highest BSA (1.94 ± 0.18 m²; P < .0001 versus without RFR; P = ns versus with RFR), basal GFR (123 ± 20 ml/min; P < .0001 versus subjects without RFR; P < .0001 versus with RFR) and weight (82.1 ± 13.2 kg; P < .0001 versus without RFR; P = ns versus with RFR).

The presence or absence of RFR was associated to differences in gender, weight, BMI, BSA and basal GFR. Women with small BSA may have lower GFR and no RFR, indicating possibly a lower renal endowment even in the normal range of renal function. The use of RFR may indicate a response to a higher metabolic demand in subjects with higher renal endowment.