Inhibitory Effect of Aqueous Citrate on the Growth of Calcium Oxalate Crystals

Calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) are frequently found in urinary calculi (stones). Calcium chelation by citric acid can play a major role in chelation therapy of naphrolithiasis. COM crystals were grown in laboratory using gel growth method, and the inhibitory effect of aqueous citrate on the growth of COM crystals was studied. The results indicate that with an increase in the concentration of citrate, the mass and number of the formed crystals was gradually reduced. The crystals were characterized by Fourier transform infrared spectroscopy (FTIR) to confirm the functional groups and powder X-ray diffraction (XRD) analyses to confirm the phases of the COM and COD crystals. Scanning electron microscopy (SEM) confirmed that the morphology of the crystals changed from elongated hexagonal to tetragonal bipyramidal, which is characteristic of a change from COM to COD. This study confirms that the use of citrate can promote the formation of COD crystals and reduce the nucleation rate of COM crystals, a major component of oxalate urinary stones.