Urinary pyrophosphate excretion in renal stone formers with normal and impaired renal acidification

Abstract

A recently described method for analysis of inorganic pyrophosphate (PPi) was used to investigate urinary excretion of PPi in renal calcium stone formers with normal (n=44) or impaired renal acidification capacity (RTA; n=13) as well as in controls (n=22) of corresponding sex and age. The mean values of the 24 h urinary PPi excretion were lower in stone-forming groups than in the control group. There was no statistical difference in the mean 24-h PPi excretion between stone-forming groups with normal and with defective urinary acidification, but there was an overrepresentation of low values for PPi excretion in the latter subject group. Positive relationships existed in all subject groups between the urinary excretion of phosphate and PPi when pooled data from various conditions of phosphate intake (fasting, non-fasting, oral phosphate loading) were examined. In the fasting state the PPi excretion was similar in stone formers and controls. Oral orthophosphate loading after phosphate deprivation with aluminium hydroxide invariably caused a rise in urinary PPi excretion in all subjects, with no difference between stone formers with normal acidification, RTA stone patients and controls. The increment in urinary PPi was positively correlated to the increment in urinary phosphate but not to changes in serum phosphate. In conclusion, these results suggest that renal stone formers may have a lower daily PPi excretion compared with controls. This was most pronounced in patients with impaired renal acidification capacity and may be due to a generalized disturbed tubular function.