Renal tubular dysfunctions in patients with idiopathic calcium nephrolithiasis

To define the degree of renal tubular involvement in idiopathic calcium nephrolithiasis, 18 patients (aged 23-60 years, 15 men and 3 women, with 1-30 years of renal stone history) with normal glomerular filtration rate (GFR) and effective renal plasma flow with no history of urinary tract infection and on no dietary or drug therapy underwent the following studies: measurement of proximal tubular maximum reabsorption of glucose (Tmglucose) and secretion of para-aminohippurate (TmPAH), urinary concentrating ability after 14 h of fluid deprivation, and urinary net acid excretion following an oral dose of ammonium chloride, 0.1 g/kg of body weight. Seventeen healthy subjects in the same age range served as control. Patients with calcium nephrolithiasis, with normal renal hemodynamic functions, have significantly lower proximal tubular maximum reabsorptive and secretory functions, diminished urinary concentrating mechanism, and reduced urinary net acid excretion following an oral acid load. These tubular functional abnormalities were observed in patients with or without hypercalciuria.