Urinary calculi: review of classification methods and correlations with etiology

Current physical and chemical methods available for urinary stones analysis are critically reviewed. No one method is sufficient to provide all the clinically useful information on the structure and composition of the stones. We show that a combination of refined morphological and structural examination of stone with optical microscopy, complemented by compositional analysis using infrared spectroscopy of the core, cross-section and surface of calculi, provides a precise and reliable method for identifying the structure and crystalline composition, and permits quantification of stone components while being highly cost effective. Using such morphoconstitutional studies leads to a classification of urinary stones in seven distinctive types and twenty-one subtypes among monohydrate (whewellite) and dihydrate (weddellite) calcium oxalates, phosphates, uric acid, urates, protein, and cystine calculi. Furthermore, all of the recognized sub-types exhibit correlations with specific pathophysiologic conditions. We conclude that such morphoconstitutional refined analysis and classification of urinary calculi is of interest to properly identify the type of stone disease and provides clues to etiopathogeny.