Urinary pH: its regulation and relevance in urolithiasis metaphylaxis

Urolithiasis is a common multifactorial disease characterized by a high recurrence rate. This review is devoted to the urine pH as one of the main factors determining its lithogenic properties. It affects the excretion of lithogenic substances and stone formation inhibitors, the solubility, and the crystallization of substances involved in stone formation. The urine pH significantly affects the solubility of uric acid in urine, which decreases at a pH < 5.5. This explains the high incidence of uric acid concretions in patients with metabolic syndrome. Their insulin resistance leads to a decrease in the excretion of ammonium ions in the proximal tubules, leading to persistent urine acidification. The activity of many transport processes involved in the processing of calcium, citrates and phosphates is sensitive to changes in systemic or local pH. The data on the effect of urine pH on the solubility of calcium oxalate remain contradictory. At the same time, there is no doubt about the determining role of urine pH in the excretion of citrate, the most important stone formation inhibitor. The alkaline urine pH promotes the formation of concretions containing calcium phosphates. In conditions of constantly elevated urine pH in patients with persistent urease-producing urinary tract infection, a rapid growth of "infectious" concretions occurs. The review summarizes information on the causes of the decrease and increase in the urine pH, as well as the possibilities of medicinal and non-medicinal methods of modifying the urine pH during the prevention of stone formation recurrence.