The influence of pH on urinary ionized [Ca+]: differences between urinary tract stone formers and normal subjects
| Autor: | Christopher H. Fry, S.E.M. Langley |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | BJU International. 79:8-14 |
| ISSN: | 1464-410X 1464-4096 |
| Popis: | Objective To assess the role of pH in determining the solubility of Ca 2+ in urine from normal subjects and stone formers and to determine the conditions which cause the formation of crystalline products. Materials and methods Urine, collected from normal subjects and urinary tract stone-formers, was used in vitro. The concentration of ionized calcium, [Ca 2+ ], and pH were measured with ion-selective electrodes and the formation of crystalline products measured as the change in turbidity of the specimen. The composition of the crystalline products was analysed by infrared spectroscopy. Results The [Ca 2+ ] decreased with increasing pH and showed a biphasic relationship with a critical pH (pH n ) at which Ca-containing precipitates appeared. Compared with normal subjects, the mean (sD) value of pH n was significantly lower in urine from stone-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 (0.71), respectively. The lower pH n in stone-formers could not be explained by altered concentrations or binding properties of Ca 2+ -binding ligands. pH n increased after diluting the urine and the value of pH n was strongly dependent on the [Ca 2+ ] at a standardized pH. Conclusions Crystalline precipitates appear in urine at a critical pH which is closer to the voided pH in stone-formers than in normal subjects and might explain the greater propensity of this group to form stones. The value of pH n is critically dependent on the urinary [Ca 2+ ] and manoeuvres which reduced its concentration would reduce the tendency to form stones. |
| Databáze: | OpenAIRE |
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