birefringent crystals in urinecauses of oxalate crystals in urinecalcium oxalate crystals in urineoxalate in urineurine test calcium oxalate crystalscalcium crystals in urinecalcium oxalate in urinehexagonal crystals urinecaox crystals in urineoxalic acid in urineoxalate in urine testcalcium phosphate urine crystals