[Evaluation of maximal filtration capacity and renal functional reserve by an oral protein-loading test in adults and children]

Abstract

After a protein load, the glomerular filtration increases to a maximum called maximal filtration capacity (MFC). The difference of this value with that observed in the fasting state defines the functional renal reserve (FRR). Fifty oral protein loads have been performed in 16 controls (13 adults and 3 children) and 31 patients with kidney disease or hypertension (22 adults, 9 children, 3 tests being performed twice). The load consisted in the adults of 80 g of various proteins. In the children the load consisted in the 100% of the protein intake recommended of the whole day. The urinary samples were made hourly during the 5 hours following the beginning of the meal. The MFC was not always observed during the 2 hours following the end of the meal. However the mean of the clearances measured during these 2 hours allowed an acceptable evaluation of the FRR in 42 out of 50 cases and had the advantage to reduce the errors linked to incomplete bladder voiding. In the adult controls the mean of hourly determined MFC is 156 +/- 27 ml/min, the mean of the clearances measured on the 2 hours following the meal is 136 +/- 21 ml/min and the fasting clearance 96 +/- 22 ml/min. The FRR is null in all patients with a nephropathy with a fasting clearance below 40 ml/min. It is modest or null in patients with acquired or congenital solitary kidney. Three out of five patients with proteinuria have MFC and FRR higher than the mean of the patients with comparable fasting clearances but without proteinuria suggesting that proteinuria is associated with a hyperfiltration state.