Nephrolithiasis

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Overview, Causes, & Risk Factors

Kidney stone formation may result when the urine becomes overly concentrated with certain substances. These substances in the urine may complex to form small crystals and subsequently stones. Stones may not produce symptoms until they begin to move down the ureter, causing pain. The pain is severe and often starts in the flank region and moves down to the groin.

Kidney stones are common. About 5% of women and 10% of men will have at least one episode by age 70. Kidney stones affect about 2 out of every 1,000 people. Recurrence is common, and the risk of recurrence is greater if two or more episodes of kidney stones occur. Kidney stones are common in premature infants.

A personal or family history of stones is associated with increased risk of stone formation. Other risk factors include renal tubular acidosis and resultant nephrocalcinosis.

Some types of stones tend to run in families. Some types may be associated with other conditions such as bowel disease, ileal bypass for obesity, or renal tubule defects.

• Calcium stones are most common, accounting for over 75% of all stones. They are two to three times more common in men, usually appearing at age 20 to 30. Recurrence is likely. The calcium may combine with other substances such as oxalate (the most common substance), phosphate, or carbonate to form the stone. Oxalate is present in certain foods. Diseases of the small intestine increase the tendency to form calcium oxalate stones.
• Uric acid stones are also more common in men. They are associated with gout or chemotherapy. Uric acid stones make up about 10% of all stones.
• Cystine stones may form in persons with cystinuria. It is a hereditary disorder affecting both men and women.
• Struvite stones are mainly found in women as a result of urinary tract infection. They can grow very large and may obstruct the kidney, ureter, or bladder.

Other substances may crystallize, precipitate, and form stones.