MEASUREMENT OF METASTABILITY, GROWTH AND AGGREGATION OF CALCIUM-OXALATE IN NATIVE URINE - A NEW APPROACH FOR CLINICAL AND EXPERIMENTAL STONE RESEARCH

Nucleation, growth and aggregation are thought to be the most importan t crystallization processes in stone formation. Since crystallization properties change with urinary dilution, centrifugation and filtration , crystallization should always be studied in freshly voided and not p retreated urine. Recently we developed an automated method where calci um oxalate crystallization is induced in native urine by an exogenous oxalate load and nucleation and growth are monitored by an ion-selecti ve calcium electrode. The method has now been supplemented with the sp ectrophotometric measurement of crystal aggregation. Repeated experime nts in the same urine with different oxalate loads enable the determin ation of the critical oxalate additionable to induce crystallization ( metastable limit) and the calculation of an oxalate load-independent g rowth rate constant. Preliminary results obtained in the native urine of healthy controls showed an extremely high limit of metastability an d a complete absence of crystal aggregation. These findings may explai n why, despite frequent urinary calcium oxalate supersaturation, healt hy people do not form stones.