Abstract
We measured the solubility of uric acid and monosodium urate in the concentrated urine obtained by the Fishberg concentration test and obtained fairly reproducible results. The solubility of uric acid in the concentrated urine samples showed an exponential increase with increasing pH. The solubility of monosodium urate showed a inverted V-shaped curve with a peak near pH 5.5. On the acidic side of this peak, the solubility decreased rapidly with decreasing pH, but on the alkaline side, it decreased gradually with increasing pH.
These results indicate the necessity of re-evaluating the concept of urine alkalization. The greater portion of uric acid exists in the form of urate in the urine, because its pKa, about 5.47, is in the lower half of the range of physiological changes in urine pH. Therefore, it is important to determine the solubility of urate, as well as that of uric acid. Since uric acid ions are affected by corresponding cations in the pH range on the alkaline side from the pKa, the solubility of total uric acid must be considered, with emphasis placed on urate, rather than uric acid.
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Shimizu, T., Nishikawa, M. & Matsushige, H. 139 THE SOLUBILITY OF URIC ACID AND MONOSODIUM URATE IN URINE. Pediatr Res 24, 134 (1988). https://doi.org/10.1203/00006450-198807000-00163
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DOI: https://doi.org/10.1203/00006450-198807000-00163