Metabolic risk factors and the formation of urinary stones. Study X: Lithogenic properties of phosphaturia in men and women.

Introduction. The role of hyperphosphaturia in calcium phosphate stones formation, including gender-specific features of its lithogenic properties in male and female patients, is still unclear. In this study, we investigated the effect of varying degrees of phosphaturia in stone formers men and women on metabolic parameters and the urinary stones frequency. Materials and methods. We examined 981 stone formers (438 men and 543 women aged 18 to 79 years). To assess the lithogenic activity of phosphaturia in stone formers men and women, the values of phosphate excretion (in mmol/day) were ranked in ascending order and divided into 10 equal parts (ten 10%-х percentilesей). In each of the ranges, the percentage distribution of types of urinary stones and biochemical parameters of urine and blood were determined. Results. As the degree of phosphaturia increased from minimum to maximum values the number of calcium oxalate stones among male patients increased 1,3-2,3 times (p=0,0001), and the frequency of detection of oxalate stones increased 1,61 times (p=0,0247), in contrast to women. In women, the proportion of carbonatapatite stones increased by 1,3-2,9 times (p<0,0001), and the carbonatapatite stones frequency from with an increase in phosphaturia was 1,462,21 times higher than in men (p<0,0001).The involvement of calciuria in calcium phosphate lithogenesis was marked by the accumulation of calcium phosphates in bimineral oxalate-phosphate calcium stones, which was 1,4-1,45 times more active in women than in men under calcium excretion of 3,63-5,1 mM/day and decreased with a further increase in calciuria (p=0,054). An important additional factor in the activation of phosphate lithogenesis should be considered alkalinization of urine, which is indicated by a direct correlation between the accumulation of phosphate in stones and urine pH in men (rs=0,265, p=0,00028) and women (rs=0.164, p=0.0037). However, in women, active phosphate lithogenesis occurs at low values of phosphaturia. Thus, the formation of carbonatapatite stones mainly depends on the excretory activity of phosphates and calcium at alkaline urine pH values. This process is most pronounced in female patients, which indicates different mechanisms of calcium phosphate lithogenesis, depending on the gender of stone formers. The incidence of carbonatapatite urolithiasis in the studied age groups did not depend on the level of phosphaturia and progressively decreased in men and women with increasing patient age (p=0.0059 and p=0.00019, respectively), which is obviously associated with an increase in total number of stone formers with age. Conclusion. Phosphaturia has a certain modifying effect on the lithogenesis of calcium oxalate stones, calcium phosphate (carbonatapatite) stones and mixed calcium oxalate-phosphate stones. The lithogenic properties of phosphaturia have characteristic gender features, which are obviously able to be fully realized when interacting with other metabolic factors of stone formation, which should be taken into account when conducting personalized methaphylaxis treatment of urolithiasis.