High levels of calcium, oxalate, uric acid, or other chemicals can cause the kidneys to produce small, pebble-like kidney stones. The existence of previous stones may act as a catalyst for the development of new ones. This test will provide insight into the makeup of the stone and assist direct a treatment strategy to stop the development of stones in the future. If kidney stones have been identified as your problem, this test might be necessary. Smaller stones can leave your body through your urine. Urine can be filtered through a kidney stone strainer to extract the stone. Your doctor might ask you to bring a kidney stone that you've already passed but retained for testing.