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Objectives: To investigate the presence of calcium urate, sodium, potassium and calcium in 'pure' uric acid calculi. Methods: Ten spontaneously passed uric acid urinary calculi have been examined by stereoscopic microscopy, infrared spectroscopy, scanning electron microscopy and energy dispersive X-Ray analysis. Results: The analysis of selected uric acid calculi revealed the presence of a near-pure calcium urate in two cases and of calcium enriched urate zones in all of the samples. Furthermore, in some cases complex urates containing sodium, potassium and calcium in different proportions appeared on the surface of the uric acid calculi studied, potassium being generally predominant. Ammonium urate was not detected. Conclusions: Most urinary uric acid calculi are not pure in composition. 'Complex urates', sodium, potassium and calcium were found together in various proportions in many areas of uric acid stones.

The careful analysis of cystine calculi may be important to detect the presence of other urinary alterations (such as hyperuricosuria, hypercalciuria, hyperoxaluria or bacterial infections) that coexist with cystinuria in many patients. For this reason, in the present study, 14 human and 17 canine cystine uroliths have been studied by infrared spectroscopy (IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). According to the infrared analysis, most of the human and canine stones were composed of nearly pure cystine. However, in these calculi of apparently pure cystine, the study by SEM and EDX showed in many cases the presence of small amounts of calcium apatite. The infrared study of several samples heated at 750°C confirmed the presence of phosphate, when it was difficult to detect this component in the spectra of the original samples owing to band overlapping. Other components detected in varying proportions in cystine calculi were magnesium ammonium phosphate hexahydrate (struvite), calcium hydrogen phosphate dihydrate (brushite), calcium oxalate (mono and/or dihydrate) and, in one case, a drug (oxolinic acid). © 1999 John Wiley & Sons, Inc.

The application of infrared and Raman spectroscopic techniques to the analysis of urinary calculi is reviewed and their relative efficiency and adaptability to routine analysis are discussed. Using the classification of urinary calculi based on their main constituents, infrared and Raman spectra of calcium oxalates, phosphates, uric acid, urates, and cystine are reported. Some characteristic bands are suggested as useful for analytical purposes. References to other constituents such as drugs are included. Although this review is aimed principally at human stones, it also extends to literature references dealing with urinary calculi from canine, feline, and equine animal species.