Metabolic risk factors and formation of urinary stones. Study III: Effect of urine pH
Introduction. Acidity of urine is an important factor that can have a modulating effect on the formation of kidney stones. The formation of certain types of urinary stones (oxalate, phosphate, urate, cystine) is largely dependent on the urinary pH. However, the acidity of urine is not the only factor determining the ability urine to stone formation. The lithogenic potential of urine is the result of the interaction of various factors, both metabolic and physicochemical ones, including urine pH. Goal. The purpose of this paper is to study the effects of a physicochemical factor such as the urinary pH on the excretory activity of some lithogenic metabolic risk factors for urolithiasis, as well as the frequency and risk of formation of urinary stones of various metabolic types. Material and methods. The mineral composition of 636 urinary calculi has been studied (from 274 men and 362 women aged 16 to 77 years), as well as daily urinary excretion of urine, uric acid, phosphate and magnesium. Results and discussion. It has been shown that when urine acidity decreases below pH 6.0, the frequency of detection of oxalate urolithiasis rises, reaching a maximum at pH 5.6-5.8 and coinciding with a calcium excretion maximum. The high frequency of detection of oxalate stones in patients remains practically constant, ranging from 40.0% to 41.3%, and with a further increase in the acidity of urine up to a pH of 4.8-5.0, despite a decrease in calciuria of 1.42 times. In the pH range from 5.9-6.0 to 5.6-5.8, the increase in oxalate lithogenesis may be exacerbated by calciuria (from 4.92 to 6.29 mmol / day), which should be reduced by anti-relapse therapy. At pH values from 5.6-5.8 to 5.4-5.5, oxalate urolithiasis metaphylaxis should be mainly directed to correct urinary pH disturbances, since under these conditions even a decrease in the level of calciuria does not significantly affect the reduction in the frequency of formation of oxalate stones. The frequency of detection of urate stones increases more than 2-fold with a decrease in urine pH below 5.4-5.5 and does not increase with a maximum uric acid excretion observed at pH 5.6-5.8. This confirms leading role of low urinary pH values in urate lithogenesis in comparison with the severity of uricuria, as well as the general principles of urate lithiasis metaphylaxis. The frequency of detection of phosphate stones, represented by carbonatopatite, increases almost 2-fold at urinary pH values above 5.6-5.8 and does not decrease with a decrease in the level of calcium and phosphate excretion. This indicates the leading role of alkalinization of urine in the formation of phosphate stones and suggests that the main goal of the metaphylaxis of this type of stones should be to maintain the patient's urinary pH in the range from 5.6-5.8 to 5.4-5.5, and not control of concomitant calciuria and phosphaturia, which practically do not affect phosphate lithogenesis. The highest frequency of occurrence of struvite stones was observed at sharply alkaline pH values of urine of 7.0-9.0. In these conditions, struvite stones are found 3.5 times more often than in patients with a pH of 6.1-6.9. An increase in the frequency of occurrence of struvite stones at urine pH to 7.0-9.0 does not depend on the influence of metabolic risk factors, as the excretion of calcium, uric acid, as well as of the constituents of struvite stones, phosphates and magnesium was significantly lower than their maximum values in the urinary pH range 5,6-5,8.