Rationale for the Evaluation of Renal Functional Reserve in Living Kidney Donors and Recipients: A Pilot Study

Abstract

Background: In living kidney transplantation, preoperative donors' renal functional reserve (RFR) may correlate with postoperative residual renal function in both donors and recipients. The aim of this study was to evaluate the donors' RFR before transplantation and to compare basal and stress renal function before and after transplantation in both donors and recipients. Methods: Seven pairs of living kidney donors and recipients were considered for this observational study. RFR was measured with a renal stress test (RST) before and after the kidney transplantation through an oral protein loading test (1 g/kg of body weight). RFR was defined as the difference between the maximum value of creatinine clearance after protein load (stress glomerular filtration rate, sGFR) and baseline creatinine clearance (basal GFR, bGFR). Results: Before transplantation, a significant difference between sGFR and bGFR (p = 0.04) was observed in donors, with an RFR = 30.6 (11.9-41.5) mL/min/1.73 m². After kidney transplantation, sGFR was similar to bGFR for both donors and recipients (p = 0.13), with a limited RFR (7.9 [6.70-19.25] and 14.90 [-6.67 to 25.53] mL/min/1.73 m², respectively). The sum of the donor's and recipient's post-transplant sGFR was similar to the pre-transplant donor's sGFR (p = 0.73). Conclusion: RST is a safe, feasible, easy, and an inexpensive tool that is able to quantify RFR. In living kidney transplantation, it can be used in clinical practice to measure the original global filtration capacity of the donor's kidneys (sGFR) and to quantify the susceptibility of donors and recipients in developing postoperative kidney dysfunction. However, further studies with an adequate sample size and follow-up period are needed to test this hypothesis.

Haemodynamic or metabolic stimulation tests to reveal the renal functional response: requiem or revival?

“…First, hydration status [ 39 ] is a very important confounding variable. Spinelli et al [ 40 ] advise the use of bio-impedance measurements to identify dehydrated subjects. For this reason, most protocols adopt a strict oral hydration policy, starting with 10–20 mL/kg plain water and replacing each voided urine sample with an equal amount of oral fluids.…”

“…Because the test remains in the experimental context, it is not reimbursed. Spinelli et al [ 40 ] performed a cost calculation of a simple RFR test using cooked beef as a stimulus and four urine CrC measurements added to 8 h of a nurse’s workload. The total cost was €91 for a single RFR estimation.…”

Reserva funcional renal. Concepto y aplicabilidad potencial en la práctica clínica

“…Posterior al trasplante, la VFG basal y la VFG estimulada fueron similares tanto en los donantes como en los receptores. La suma de la VFG estimulada post-trasplante de los donantes y sus receptores fue igual a la VFG estimulada de los receptores previo a la donación, indicando que la RFR se repartió entre los receptores y sus donantes 8 .…”

“…3) Evaluación de sujetos que desean ser donantes de riñón para trasplante. Como la existencia de ERC y requerimiento de diálisis se han observado en algunos donantes años después de la nefrectomía, una evaluación cuidadosa antes de la donación debería practicarse 8 . La ausencia o reducción en la RFR indica que existe un menor número de nefrones y que los potenciales donantes tienen un mayor riesgo de desarrollar hipertensión arterial, proteinuria y ERC en el futuro 3,21 .…”

“…Los riñones están compuestos por alrededor de un millón de nefrones cada uno, los que exceden los requerimientos fisiológicos en condiciones normales. Ello permite soportar los requerimientos ante stress fisiológicos o patológicos 8 . En sujetos sanos los riñones funcionan normalmente en aproximadamente 75% de su capacidad máxima (filtración glomerular basal), pudiendo adaptar su funcionamiento a demandas metabólicas y hemo-dinámicas con el fin de mantener la homeostasis 2,3 .…”