The presence of calcium oxalate crystals is very common and generally has little clinical significance. They are found in urine with a pH between 6.0 and 7.0. The formation of calcium oxalate crystals can be caused by a combination of factors including decreased urine volume or a diet rich in oxalates (cabbage, rhubarb, spinach, tropical fruits, etc.) or calcium (dairy products). They are also found in individuals with calcium levels that are too high following prolonged immobilization, overactive parathyroid glands or bone metastases, etc.
In individuals with kidney stones, the repeated presence of calcium oxalate crystals could indicate the probable nature of the stone. It should be noted, however, that most patients with calcium oxalate crystals will never form stones.