Establishment of a Solubility Test for the Differentiation of Urine Crystals

Background:The lack of data on the solubility of certain crystals has resulted in conflicting findings.Therefore, establishing a standardized solubility test for use in clinical laboratories is essential.Methods: Calcium carbonate, calcium oxalate monohydrate, calcium phosphate dibasic, calcium sulfate, cystine, hippuric acid, leucine, magnesium ammonium phosphate, meglumine diatrizoate, tyrosine, uric acid, uric acid sodium salt, and xanthine were procured from Sigma-Aldrich Co., USA.These crystals were suspended in 30% acetic acid, 30% hydrochloric acid, 10% potassium hydroxide (KOH), distilled water, ethanol, chloroform, and ether.Their morphology and dissolution characteristics were examined under an inverted microscope.Results: The morphology and solubility of all 13 crystals were examined.Calcium carbonate, calcium oxalate, calcium phosphate, cystine, triple phosphate, tyrosine, and uric acid demonstrated solubility patterns consistent with those reported in existing literature.Meanwhile, the solubility of five crystals that lacked data was newly established.Calcium sulfate exhibited partial dissolution in 10% KOH and in distilled water at 60C.Hippuric acid, uric acid sodium salt, and xanthine dissolved in 10% KOH, while meglumine diatrizoate dissolved in distilled water and 10% KOH.Notably, the solubility patterns of calcium sulfate, hippuric acid, and leucine differed from those documented in the literature.Conclusions: This study confirmed the solubility of five crystals.Notably, the solubility of three crystals differed from that documented in existing literature.Microscopic examination, augmented by polarization, proved invaluable for distinguishing urinary crystals during the solubility test.The study findings are expected to improve the discrimination of crystals in future analyses.