Optimizing a kidney stress test to evaluate renal functional reserve

Background: Renal function reserve (RFR) describes the capacity of the kidney to increase glomerular filtration rate (GFR) in response to physiological or pathological stimuli. The scope of our study was to evaluate the optimal level of stimulation using different doses of protein load (PL) for a standard renal stress test (RST). Methods: 18 young healthy individuals were given sessions of PL with 1 and 2 g/kg body weight. Endogenous creatinine clearance was calculated. Baseline GFR (bGFR) and stress GFR (sGFR) (post-PL) were obtained; RFR is the difference between stress and baseline GFR. A p-value < 0.05 was considered statistically significant. Results: Mean bGFR was 107.97 +/- 12.33 mL/min/1.73m(2). sGFR with 1 and 2 g PL were significantly higher than bGFR in all subjects. The sGFR after 2 g PL (141.75 +/- 19.90 mL/min/1.73m(2)) was not statistically different from the sGFR after 1 g PL (142.37 +/- 22.35 mL/min/1.73m(2)). sGFR and therefore RFR were independent from the value of bGFR. Conclusions: We found no difference between 1 and 2 g/kg body weight PL to elicit sGFR. RST may be useful to predict susceptibility and risk of developing acute kidney injury and/or progression to chronic kidney disease. RST uncovers the possible loss of renal functional mass when this condition is not manifested clinically. Further studies are needed to set this hypothesis.