The influence of pH on urinary ionized [Ca⁺]: differences between urinary tract stone formers and normal subjects

Abstract

Objective To assess the role of pH in determining the formers, at 7.67 (0.62) and 7.21 (0.54), respectively, and nearer to their voided pH of 5.92 (0.70) and 6.26 solubility of Ca2+ in urine from normal subjects and stone formers and to determine the conditions which (0.71), respectively. The lower pH n in stone-formers could not be explained by altered concentrations cause the formation of crystalline products. Materials and methods Urine, collected from normal or binding properties of Ca2+-binding ligands. pH n increased after diluting the urine and the value of pH n subjects and urinary tract stone-formers, was used in vitro. The concentration of ionized calcium, [Ca2+], was strongly dependent on the [Ca2+] at a standardized pH. and pH were measured with ion-selective electrodes and the formation of crystalline products measured asConclusions Crystalline precipitates appear in urine at a critical pH which is closer to the voided pH in stonethe change in turbidity of the specimen. The composition of the crystalline products was analysed by infraformers than in normal subjects and might explain the greater propensity of this group to form stones. red spectroscopy. Results The [Ca2+ ] decreased with increasing pH andThe value of pH n is critically dependent on the urinary [Ca2+] and manoeuvres which reduced its concenshowed a biphasic relationship with a critical pH (pH n ) at which Ca-containing precipitates appeared.tration would reduce the tendency to form stones.

The physicochemical basis of urinary catheter encrustation

“…In a previous study it was shown that pH n in urine collected from urinary tract stone‐formers was significantly more acid than that from normal subjects [ 10]. The shift in pH n was strongly dependent on the total [Ca] as well as ionized [Ca 2+ ] at a standard pH; the pH n was lower at higher Ca levels in the stone‐forming group.…”

“…The voided urinary pH (pH v ) was measured in a urine sample drawn into a glass syringe within 45 s of micturition, to minimize CO 2 loss [ 10]. Urine was submitted for routine bacteriological culture and to test for urease activity.…”

“…However, the decline in urinary [Ca 2+ ] with increasing pH is not linear and it has been shown that there is a critical pH value in urine above which Ca 2+ remains less readily in solution and precipitates as crystalline complexes [ 9]. In a study of urinary tract stone‐formers it has been shown that this critical pH is more acid than in those not forming stones, approaching the normal pH of urine and hence enhancing the likelihood of crystalline precipitates [ 10]. The factors which determine the relationship between the pH, [Ca 2+ ] and precipitation are unclear.…”

“…<5%) by changes in pH between 4.5 and 8.0, nor by variation of [Na], [K], [Mg] more acid than in those not forming stones, approaching the normal pH of urine and hence enhancing the likeli-or macromolecular concentrations over the ranges encountered in the urine samples. hood of crystalline precipitates [10]. The factors which determine the relationship between the pH, [Ca2+] and precipitation are unclear.…”

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

“…Whereas urinary pH and Ca 2+ are inversely related [6, 7], both systemic and urinary acidosis may inhibit renal citrate excretion if citrate reabsorption and metabolism in the proximal tubule become up-regulated in order to counteract imbalanced acid–base status [1, 8]. …”