Kidney stones are crystal-like structures formed in the various parts of the urinary tract. Stones start small and gradually grow larger. Stone formation, shape and growth are dependent on the total amount and types of crystals and all chemicals in the urine. It is believed that growth can be speeded by chemicals in the urine called "promoters" or slowed or stopped by other chemical "inhibitors". Stones nearly always form in the kidney, where they may remain without symptoms and do not require treatment. They may cause obstruction or break loose and try to pass with the normal flow of urine through the urinary tract. More commonly, a stone will enlarge or move and cause pain and obstruction. The pain of trying to pass a kidney stone has been described as the most severe pain in the back, side or abdomen that a person may experiece. The pain may be steady or come in waves and may be associated with nausea, vomiting and blood in the urine.
Approximately one person in 200 will form a kidney stone this year, which will total more than one million cases in the United States. Approximately 80% of the stones will pass spontaneously, while the remaining 20% will need treatment. If a person forms a kidney stone, there is a 50% chance of another stone forming in 5-10 years without treatment.