Crystallization rules of calcium oxalate crystals in lithogenic urine and in healthy urine in vitro

Crystallization of calcium oxalate (CaOxa) was comparatively studied in vitro in diluted lithogenic urine and in diluted healthy urine by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. In healthy urine, the crystallization was a growth-controlled process in the early stage of crystallization and a nucleation-controlled process in the middle and late stage. However, the crystallization of CaOxa was always a growth-controlled process in the lithogenic urine. That is, the size of CaOxa particles grow gradually and at last large size of CaOxa stones formed. Comparing the CaOxa crystals grown in lithogenic urine and in healthy urine, three differentiations were observed. First, the average particle size of CaOxa crystals precipitated in lithogenic urine is larger than that in healthy urine. Second, the morphology of calcium oxalate monohydrate (COM) crystals changes from sharp hexagonal in lithogenic urine to round and blunt in healthy urine. Third, calcium oxalate dihydrate (COD) crystals were induced in healthy urine. The results in this study may provide important clues to cure urinary stones.