SummaryThe concept of renal functional reserve (RFR) was introduced in the 80’s. The renal functional reserve was defined as the ability of the kidney to increase Renal Plasma Flow (RPF) and Glomerular Filtration Rate (GFR) after a stimulus as a protein load. The absence of RFR defines a state of hyperfiltration which seems to be a detrimental factor for the progression of renal failure.The measure of RFR by a protein load test is thus a mean to detect glomerular hyperforation and allows to give adequate diet prescription.