Infrared analysis of renal calculi: a comparison with conventional techniques

The analysis of renal calculi is an oft-neglected corner of clinical biochemistry. This study compares results obtained by the conventional qualitative methods with results from quantitative and infrared methods and also investigates the role of x-ray diffraction analysis. Infrared spectroscopy, using a KBr disc technique, was found to be the single most useful method, being fast, simple to learn, using little sample, and in general permitting positive identification of most of the components found in renal calculi. A major advantage is that this method has approximately equal sensitivity for oxalate and phosphate, unlike the wet chemical methods. Infrared analysis is also useful in identifying the spurious materials sometimes submitted as renal calculi. X-ray diffraction analysis is not a technique that is routinely available, but it does provide information not given by other methods, eg, distinguishing Ca(COO)2 . H2O from Ca(COO)2 . 2H2O. For complete analysis a combination of methods was adopted; carbonate is tested for using a microchemical technique, calcium, magnesium, and phosphate are quantitated by routine methods, and infrared analysis is used to detect oxalate and organic components. It must be emphasised that any method is only as good as the sample used, and different areas of the calculus must be analysed separately if useful results are to be obtained.