Analysis of urinary calculi

Urinary calculi are often small (< 5 mg) and can be composed of many very different constituents. The highly variable composition has lead to the development of many different methods of calculi analysis. In general the analytical methods can be divided in chemical and physical methods. Chemical methods are destructive and need several mg of sample. The smallest stones can not be analyzed with chemical methods. Qualitative and semi-quantitative chemical analysis methods are not accurate and can lead to clinical significant errors. Quantitative, instrumental, chemical analysis is accurate and makes no clinical significant errors, but these consume too much sample. None of the chemical methods of stone analysis makes it possible to distinguish the mineral constituents with similar chemical composition, e.g. the calcium phosphates, from one another and they usually can not identify "unexpected" stones. Physical methods need less sample than chemical methods and physical methods can distinguish the different minerals in the stones. Thermal analysis can give quantitative results but needs relatively much sample. Optical methods can analyze a few grains of stone but gives only qualitative results. Both methods can not be used to analyze an "unexpected" stone. Best suited methods for the analysis of calculi are X-ray diffractometry and IR spectroscopy. X-ray diffractometry can detect crystalline minerals in low concentrations. IR spectroscopy can detect both crystalline and amorphous minerals. Both methods can be used for semi-quantitative stone analysis and can analyze less than one mg of stone sample. X-ray diffractometry and IR spectroscopy are also the best methods to identify "unexpected" stone constituents.