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

Abstract

BackgroundHypercalciuria 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.MethodsWe 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.ResultsTotal 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 Ca2+/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.ConclusionsCompared to controls, stone-formers with hypocitraturia demonstrated a higher urinary Ca2+ concentration, but this was proportional to calciuria. The large individual variability in urinary Ca2+ 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.

Hypocitraturia Is an Untoward Side Effect of Synthetic Human Parathyroid Hormone (hPTH) 1-34 Therapy in Hypoparathyroidism That May Increase Renal Morbidity

“…Conversely, alkalosis increases citrate excretion. The definition of hypocitraturia is ill‐defined, with some proposing absolute excretion cut‐off and others using calcium/citrate, citrate/calcium, and citrate/creatinine ratios . As hypercalciuria is an important comorbidity of hypoparathyroidism and its therapy, we chose to focus on the UCa/Ucit ratio, with the understanding that the risk for renal calcification is more likely related to the relative concentrations of these two analytes, rather than their absolute excretion.…”

Urinary citrate excretion in healthy children depends on age and gender

“…Many authors have postulated that not only the absolute urinary calcium or citrate concentrations, but alternatively the relative proportion of the two, determine the risk of stone formation [ 20 , 25 , 26 ]. It has been shown that a urinary calcium/citrate index of 0.326 mg/mg can discriminate well between pediatric stone formers and healthy controls [ 20 ].…”

Urinary calcium excretion in children with monosymptomatic enuresis

“…Another aspect of our study was to examine the correspondence between Ca 2+ and/or calciuria in pediatric diseases. Recent data indicate increased Ca 2+ concentration in stone-formers [ 28 ]. The urinary concentration of Ca 2+ is largely pH-dependent.…”