Factors modulating the pH at which calcium and magnesium phosphates precipitate from human urine

The factors controlling the rate at which crystalline bacterial biofilms develop on indwelling bladder catheters are poorly understood. It is known that normally the pH of voided urine (pH_v) is lower than the pH at which calcium and magnesium phosphates come out of urine solution (pH_n). In patients who develop infections with urease producing bacteria, however, the pH_v rises above the pH_n and precipitation of the phosphates occurs in the urine and the biofilm. The aim of this study was to examine ways of manipulating the pH_n of urine so that more of its calcium and magnesium remain in solution under alkaline conditions. The experimental data show that pH_n can be elevated by decreasing the calcium, magnesium and phosphate concentrations. Increasing the fluid intake of a human subject so that the urinary calcium fell from 120 mg/l to 25 mg/l, for example, resulted in the pH_n increasing from 6.48 to 8.22. The addition of citrate to urine also produced a rise in the pH_n. The daily consumption of 500 ml of fresh orange juice increased urinary citrate concentrations from 0.35 to around 1.21 mg/ml and the pH_n rose from 7.24 to 8.2. The pH_n of urine is thus a highly variable parameter. It can be manipulated by controlling the urinary concentrations of magnesium, calcium, phosphate and citrate ions. We suggest that increasing fluid intake with citrate containing drinks would reduce the extent of encrustation on catheters in patients infected with urease producing bacteria.