Analysis of urinary calculi; a quality control programme

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Abstract
Results of the first Nordic quality control programme on urinary calculi are described. The programme included nine specimens, nine components and 57 laboratories participated. Most of the specimens were mixtures of selected human calculi. Of the laboratories, 67% used a binary scale for the results (“qualitative”); 80% of the laboratories were unable to carry out the analysis on 10 mg material or less. For most components false positive results were rare. Oxalate and calcium(II), however, were exceptions. Results on “mixed stones” were unsatisfactory; frequently 20% of the results were wrong. The fraction of false negative results is 0.10 for cystine and urate, and is generally higher for other components. No difference between the reliability of infrared spectrometry and of wet chemistry is observed. An ordinary internal quality control scheme is suggested to facilitate improvements of the routine analytical performance. Some ideas of the analytical strategy are discussed. The drawbacks of results from a binary scale are stressed, and it is suggested that the examination of urinary calculi be carried out using techniques which give results on continuous scales. At the same time the number of components for analysis in the routine programme may be reduced.