A kidney stone is like a small rock that begins as a tiny crystal formed from chemicals in the urine. Several crystals may stick together to form a stone. A stones originates in one of the many the microscopic urine collecting kidney tubules, but as it gets larger, it passes along with the urine into the larger drainage system of the kidney, the funnel shaped renal pelvis, and then along the narrow ureter toward the bladder. This is usually the time the stone causes pain and or bleeding.

The four main types of kidney stones listed below have a different cause and may need a different kind of prevention. The type of stone is determined by analyzing fragments passed in the urine after lithotripsy.

Calcium stones: 90% of stones contain calcium combined with another mineral. The commonest type of calcium stone is calcium oxalate. Calcium may also combine with phosphate, forming insoluble crystals. Crystal formation is dependent on three things: temperature, pH, and concentration. (We can't do much to change the temperature inside our bodies, so the only two things we can control are pH and concentration). Normally, urine contains substances that inhibit crystal formation, so some people will form stones, and others with the same concentration and pH will not. One way to control concentration is by diluting with water. Drinking 8 to 10 glasses of water per day or more will lower the mineral concentration enough to reduce or eliminate further stone formation. By reducing the intake of oxalate (dark green vegetables, soy products, nuts, and chocolate) and phosphate, (avoid adding table salt, less beef, pork, and poultry, and increased dietary fiber), some people can reduce their risk of forming more stones. There are many medical diseases, such as hyperparathyroidism, several kidney diseases, and intestinal bypass surgery that may result in high concentrations of minerals in the urine. People with these diseases eat normal amounts of calcium but absorb too much of it from their intestines. In other people the kidney leaks large amounts of calcium in the urine, even on a calcium restricted diet. As you can see, this is a complicated topic, so please consult your doctor for more information.

Uric acid stones: One end product of protein metabolism is uric acid. Uric acid can form crystals with or without combining with other minerals. These stones are unique, however, in that they tend to form in acid urine (pH of 5 or 6) and are soluble in alkaline urine (pH of 7 or 8). High protein diet may contribute to this type of stone. These stones can frequently be prevented by a combination of: a. high fluid intake (four quarts of water per day); b. allopurinol, a drug that lowers uric acid concentration; c. medication such as Shohl's solution to alkalinize the urine (increase the urinary pH to 7).

Cystine stones: account for 1% of all stones. They are usually found in young individuals who have a genetic defect in their metabolism of protein, so that they secrete high concentrations of the poorly soluble amino acid cystine in the urine. Patients with this disease need ongoing, highly individualized treatment for the duration of their lives.

Ammonium magnesium phosphate stones (Struvite): These stones are uncommon and usually are associated with chronic urinary infection. Treatment is aimed at removal of all of the stone present and treatment of the infection with antibiotics.
There are other rare stones such as xanthine, triamterene, silicate, and matrix calculi. Details about these calculi can be found in the resources listed at this web site.
In summary, recurrence of kidney stones can often be prevented by making a few lifestyle changes. Appropriate urine and blood tests will enable your physician to offer specific dietary and or medication advice.