What Causes Kidney Stones?

Kidney stones often have no definite, single cause. A number of factors, often in combination, create the conditions in which susceptible people develop kidney stones.

Kidney stones form when the components of urine fluid and various minerals and acids are out of balance. When this happens, your urine contains more crystal-forming substances, such as calcium, oxalate and uric acid, than the available fluid can dilute. At the same time, your urine may be short of substances that keep crystals from sticking together and becoming stones. This creates an environment in which kidney stones are more likely to form.

Types of kidney stones
Most kidney stones contain crystals of more than one type. Types of kidney stones include:
* Calcium stones. Most kidney stones are calcium stones, usually in the form of calcium oxalate. High oxalate levels can be found in some fruits and vegetables, as well as in nuts and chocolate. Your liver also produces oxalate. Dietary factors, high doses of vitamin D, intestinal bypass surgery and several different metabolic disorders can increase the concentration of calcium or oxalate in urine. Calcium stones may also occur in the form of calcium phosphate.

* Struvite stones. Struvite stones form in response to an infection, such as a urinary tract infection. Struvite stones can grow quickly and become quite large.

* Uric acid stones. Uric acid stones can form in people who are dehydrated, those who eat a high-protein diet and those with gout. Certain genetic factors and disorders of the blood-producing tissues also may predispose you to uric acid stones.

* Cystine stones. These stones represent only a small percentage of kidney stones. They form in people with a hereditary disorder that causes the kidneys to excrete excessive amounts of certain amino acids (cystinuria). * Other stones. Other, rarer types of kidney stones can occur.

Knowing your type of kidney stone helps to understand what might have caused the stone to form and may give clues as to what you can do to reduce your risk of getting additional kidney stones.