[Results of quality control surveys for urinary calculus analyses]

In 1980 and 1981, four quality control surveys for urinary calculus analyses were carried out, within the framework of external quality controls of the Deutsche Gesellschaft für Klinische Chemie. During these quality control surveys the participating laboratories received a total of 16 samples (eight pure substances and eight mixtures of two components), to be analyzed qualitatively and quantitatively. For the qualitative analyses, a laboratory could provide simplified descriptions of the analytes - for example, without stating the number of molecules of the water of crystallization; or, to the extent permitted by the mode of analysis, the exact chemical composition could be presented. Of 1283 analyses, 818 (64%) attained the goals of the simplified analysis. The most frequent errors in chemical analyses were false negative and false positive results for calcium oxalate, and false negative results for calcium phosphate. Laboratories using analysis by infrared spectroscopy also submitted the biggest proportion of incorrect analyses for these components. The most reliable results were produced by X-ray-diffraction: 86% of the results in this category represented correct differentiated analyses. The generally accurate results achieved by some participants using chemical analysis suggest, however, that - in addition to the principle of analysis used - the qualification of the operator is an important determinant in the reliability of the results.