Urates in the kidney, Light micrograph (LM). High levels of uric acid in the body may cause crystal to form. These uric acid crystals combine with other substances in the body and create a solid mass. The mass keeps growing. It may stay in the kidney or move down the urinary tract and settle in the ureter. If the stones are very small, they may pass out of your body in your urine without too much pain. But if they don't pass, they cause urine to back up in the kidney, ureter, bladder or urethra. This may lead to pain and other symptoms. Magnification x60 when printed 10cm wide.