Kidney stones. The result of the build-up of crystallized salts and minerals such as calcium in the urinary tract, kidney stones (also called calculi) also can form after an infection. If kidney stones are large enough to block the kidney or ureter, they can cause severe abdominal pain. But the stones usually pass through the urinary tract on their own. In some cases, they need to be removed surgically, or treated with medication or modifications to the diet. Sometimes the first symptoms are pain and blood in the urine. Kidney stones are more common in adults than they are in kids.