We evaluated the influence of acidification, alkalization and storage at 4–8 °C on the results of estimations of sodium, potassium, chloride, phosphate, magnesium, urea, uric acid, creatinine, amylase and total protein in urine. We used 24–hour urine samples obtained from 21 hospitalized patients. Except chloride we applied methods most frequently used in the Czech Republic (used in 60–90% Czech laboratories). The assessment of combined influences of introduced factors is the aim of this study. Such a comprehensive approach to these problems is not well documented because only influences on individual analytes are found in the literature. Statistical significance at the 95% (T-test) confidence interval was used as criterion for the magnitude of changes. Acidification by 6 mol/l HCl to pH Ł 2.0 fully eliminated the catalytic concentration of amylase and strongly influenced the concentration of total protein – we estimated a change of + 55% ± 165% (mean ± SD). Alkalization by 5 mol/l NaOH to pH ł 8.0 caused significant changes in estimation of magnesium, calcium, amylase and total protein, but surprisingly not of phosphates. Storage (7 days at 4–8 °C) combined with effects of acidification or alkalization led to significant changes in estimation of magnesium, calcium, phosphates, uric acid and total protein. Urine samples without addition of acid or hydroxide should always be used for quantification of amylase and total protein. Acidified samples should be used for estimation of calcium, phosphates, magnesium. These samples can be also used for estimation of sodium, potassium, urea and creatinine. Alkalized samples should be used for uric acid and they also can be used for potassium, chloride, urea and creatinine. We recommend to avoid the storage of samples for assessment of uric acid, total protein and creatinine, while the other analytes have a minimal stability of 7 days.

        Key words: routine analytes, urine, estimation, pH adjustment, storage.