CALCULATION OF TITRATABLE ACIDITY FROM URINARY STONE RISK-FACTORS

Using urine samples and standard solutions, this study demonstrates th at the existing procedure for measuring titratable acidity in the urin e is not reliable and may result in overestimates of up to 25%. The ac curacy is affected by loss of CO2, the presence of uric acid crystals, and the precipitation of calciumphosphate phases during the titration . A method is presented for calculating titratable acidity, using a nu mber of routinely-measured urine components and a computer program for calculating complex equilibria in the urine. The calculated titratabl e acidity is shown to be more reliable then the measured one. The resu lts are compiled in a nomogram from which the titratable acidity can b e directly read. When the parameters of urine pH, PO4 content and PCO2 are used, the accuracy of the nomogram is > %% for urine samples with a pH value above 6.0 and >89% for urine samples with a pH value below 6.0. For all samples, the accuracy is improved to > 97% when the nomo gram using uric acid and citrate content is used in additionally.