In most people, the kidneys flush out the extra calcium with the rest of the urine. People who have calcium stones keep the calcium in their kidneys. The calcium that stays behind joins with other waste products to form a stone. If you tend to form uric acid stones, you may need to cut back on the amount of meat you eat. Cystine is one of the building blocks that make up muscles, nerves, and other parts of the body.
Cystine can build up in the urine to form a stone.
The disease that causes cystine stones runs in families. Kidney stones may be as small as a grain of sand or as large as a pearl. Some stones are even as big as golf balls. Stones may be smooth or jagged. They are usually yellow or brown.