Prevalence of Hypocitraturia and Hypopyrophosphaturia in Recurrent Calcium Stone Formers: As Isolated Defects or Associated with Other Metabolic Abnormalities

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Abstract
Several underlying metabolic abnormalities may be present in patients with recurrent calcium calculus disease (RCCD). The aim of this study was to determine the prevalence of deficiencies of 2 well-known potent inhibitors of crystal formation and growth, citrate and pyrophosphate, in the various metabolic subgroups and as single defects. In 107 patients with RCCD, urinary citrate was significantly decreased in all metabolic subgroups with 49% of patients having hypocitraturia (2.53 ± 1.19 mmol/24 h) versus controls (3.44 ± 0.96 mmol/24 h; p < 0.001). Reduced pyrophosphate: creatinine ratios were present in all the patient subgroups, and 48% of all patients had reduced ratios (1.68 ± 1.68 vs. 3.10 ± 2.66 in controls; p < 0.01). There was no correlation between citrate and pyrophosphate concentration. Isolated hypocitraturia was found in 11.2%, reduced pyrophosphate: creatinine ratios as the single defect in 11.2% and a combination of both in 12.1% of patients. Thus inhibitor defects play an important role in patients with RCCD and frequently occur as isolated biochemical defects.