Kidney Stones

What is a kidney stone?
A kidney stone is a hard mineral and crystalline material formed within the kidney or urinary tract. Kidney stones are a common cause of blood in the urine and often severe pain in the abdomen, flank, or groin. Kidney stones are sometimes called renal calculi. One in every 20 people develops a kidney stone at some point in their life.
The condition of having kidney stones is termed nephrolithiasis or urolithiasis.
What causes kidney stones?
Kidney stones form when there is a decrease in urine volume or an excess of stone-forming substances in the urine. The most common type of kidney stone contains calcium in combination with either oxalate or phosphate. Other chemical compounds that can form stones in the urinary tract include uric acid and the amino acid cystine.
Dehydration through reduced fluid intake or strenuous exercise without adequate fluid replacement increases the risk of kidney stones. Obstruction to the flow of urine can also lead to stone formation. Kidney stones can also result from infection in the urinary tract; these are known as struvite or infection stones.
Men are especially likely to develop kidney stones, and whites are more often affected than blacks. The prevalence of kidney stones begins to rise when men reach their 40s, and it continues to climb into their 70s. People who have already had more than one kidney stone are prone to develop more stones. A family history of kidney stones is also a risk factor for the development of kidney stones.
A number of different conditions can lead to kidney stones:
Gout results in an increased amount of uric acid in the urine and can lead to the formation of uric acid stones.
Hypercalciuria (high calcium in the urine), another inherited condition, causes stones in more than half of cases. In this condition, too much calcium is absorbed from food and excreted into the urine, where it may form calcium phosphate or calcium oxalate stones.
Other conditions associated with an increased risk of kidney stones include hyperparathyroidism, kidney diseases such as renal tubular acidosis, and some inherited metabolic conditions including cystinuria and hyperoxaluria. Chronic diseases such as diabetes and high blood pressure (hypertension) are also associated with an increased risk of developing kidney stones.
People with inflammatory bowel disease or who have had an intestinal bypass or ostomy surgery are also more likely to develop kidney stones.
Some medications also raise the risk of kidney stones. These medications include some diuretics, calcium-containing antacids, and the protease inhibitor Crixivan (indinavir), a drug used to treat HIV infection.