Role of inhibitor deficiency in urolithiasis. I. Rationale of urinary magnesium, citrate, pyrophosphate and glycosaminoglycan determinations.

Between October 1988 and March 1990, 173 urinary stone patients (average age 38.3 years) were evaluated metabolically, especially with regard to urinary magnesium, pyrophosphate (Ppi) citrate and glycosaminoglycans (GAG). 25 healthy subjects served as controls. Inhibitory deficiency was found to be the most frequent causal factor in our series, with an incidence of 48.7% in first-time stone formers and 51.08% in recurrent urolithiasis (p less than 0.1). Deficient citrate levels were present in 46.56%, hypomagnesiuria in 24.4%, hypopyrophosphaturia in 10.7% and deficient GAG in 2.7% of the patients. Deficient urinary Ppi was seen in only 2.7% of the stone formers as the only metabolic defect, while deficient GAG was never the only causal factor. All 4 inhibitors showed no correlation with age, sex, activity of stone disease, stone weight and burden. There were no statistically significant differences with controls. We think that routine metabolic evaluation must be performed both in recurrent patients and first-time stone formers and must include urinary citrate and Mg determinations in every case. Urinary Ppi should be determined in selected cases and GAG determinations are irrational.