The composition of urinary stones analysed by infrared spectrophotometry and the precipitation of calcium phosphates from saturated solutions.

Of 205 consecutively analysed urinary stones, two-thirds were from men, which reflected the male: female ratio of urolithiasis cases at this hospital in the period of the study. Phosphate was found in 69.9% of the stones from male patients and in 94.2% of those from female patients. The phosphate in the urinary stones consisted of hydroxylapatite, carboxylapatite and/or MgHN4PO4. CaHPO4 could be demonstrated in only six of the 205 stones. Oxalate was present in 59.6 and 39.1% of the stones from males and females, respectively. Calcium phosphates from saturated solutions precipitated mainly as hydroxylapatite at pH levels above 5.47. Only below this level did CaHPO4 become visible in infrared spectrophotometry analysis. The solubility of calcium phosphates greatly increased with lowering of the pH. Increasing the ionic activity of the saturated solution with sodium chloride increased the solubility of calcium phosphates only to a limited extent.