Renal functional reserve (RFR) is defined as the capacity of the kidneys to increase their glomerular filtration rate (GFR) in response to physiological or pathological stimuli.
The GFR can acutely increase following a high-protein meal or systemic infusion of amino acids, reflecting the kidney’s ability to augment its function under stress.
RFR is typically measured as the difference between baseline GFR and the peak GFR achieved after a protein load or other stimulatory challenge, and it magnitude of this increase can provide insights into the functional capacity of the kidneys beyond their resting state.
The kidney has the capacity to compensate or increase its function in states of either high metabolic demand or intrinsic kidney disease, and renal functional reserve represents increased renal plasma flow mediated by renal vasodilation, predominantly within the pre-glomerular arterial vascular.
The PROTECTION trial of an infusion of an amino acids was demonstrated to have a protective effect on kidney function after cardiac surgery.