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.