Correspondence between Ca2+ and calciuria, citrate level and pH of urine in pediatric urolithiasis

Abstract

Background: Hypercalciuria and hypocitraturia are considered the most important risk factors for urolithiasis. Citrate binds to urinary calcium to form a soluble complex which decreases the availability of ionized calcium (Ca2+) necessary for calcium oxalate formation and phosphate crystallization. The aims of this study were to assess the Ca2+ fraction in relation to total calciuria, citraturia and urinary pH and to determine whether urinary Ca2+ concentration is a helpful biomarker in metabolic evaluation of children with urolithiasis. Methods: We collected 24-h urine samples from 123 stone-forming children and adolescents with hypocitraturia and from 424 healthy controls. Total calciuria (total calcium, Catotal), Ca2+, pH, citrate, oxalate and Bonn Risk Index (BRI) were assessed and compared between the two groups. Results: Total calciuria and Ca2+ content were higher in stone-formers than in the healthy children. In both stone-formers and controls, Ca2+ content was inversely related to citraturia and urinary pH, whereas the Ca 2+/Catotal ratio differed slightly between the groups. A large variability in Ca2+ level was found across individuals in both groups. The BRI increased with increasing calciuria and urine acidity. Conclusions: Compared to controls, stone-formers with hypocitraturia demonstrated a higher urinary Ca2+ concentration, but this was proportional to calciuria. The large individual variability in urinary Ca 2+ content limits its practical use in metabolic evaluation of children with urolithiasis. However, the Ca/Citrate ratio may be a useful clinical tool in evaluating children with urolithiasis. © 2013 The Author(s).