Quantitative urinalysis with a common predilution on a DuPont Dimension.

Urine was quantitatively analysed for sodium, potassium, creatinine, calcium, urea, uric acid, inorganic phosphate and magnesium in one manual central predilution. The analysis was implemented on a DuPont Dimension and the results were compared with those obtained with our analysers currently in use. Based on modified serum methods and their assessed linearities, the 8 urine constituents were analysed with high accuracy and reproducibility in a 6-fold diluted urine with DuPont reagents. The Dimension method correlated well with flame photometry for sodium and potassium; with the EPOS analyser for creatinine, calcium, uric acid, urea and inorganic phosphate; with atomic absorption spectroscopy for magnesium. All between-run coefficients of variation were smaller than 5%, except for the analysis of sodium in the lower part of the measurement range. However, a dilution ratio of 6 is an acceptable compromise when these 8 constituents are determined collectively from a common predilution, thereby covering the complete measurement ranges for these analytes in urine specimens. An additional dilution step is necessary for only a few urine samples (fewer than 1% of samples for calcium and urea and fewer than than 2% for inorganic phosphate). The combined analysis of these 8 constituents can be carried out only on untreated urine samples. Currently recommended pretreatments, such as acidification for calcium and inorganic phosphate analysis, and uric acid analysis under alkaline conditions, can be avoided.