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Kidney Stones

Passing kidney stones can be an extremely painful process that no one wants to repeat. But patients who have experienced kidney stones have a 50 percent chance of recurrence within 10 years. The Mayo Clinic Health Letter covers how kidney stones are formed, treatment options, and ways to reduce the risk for a repeat.

Kidney stones are made up of crystal-forming minerals in the urine. Normal urine contains substances that inhibit crystal formation. However, if urine is too concentrated or if the crystal-preventing compounds aren't working properly, crystals may gradually accumulate and grow to form one or more kidney stones.

Most kidney stones pass naturally through the ureters (tubes that connect the kidney to the bladder), through the bladder, and then out in the urine. Passing a kidney stone may take hours or weeks. Most often, the process takes seven to 14 days. Small stones may not be a big bother. Larger ones can cause extreme pain, typically on the side and the back, just below the rib cage, and radiating to the lower abdomen and groin. There are a variety of treatment options, from pain management to surgical removal of the stone.

Once the stone has passed, the focus switches to prevention. Prevention strategies depend somewhat on the composition of kidney stones. About 70 percent are formed primarily of calcium oxalate. Others are formed mainly from calcium phosphate, uric acid, or struvite stones. Recommendations for prevention of kidney stones in most people may include:

• Drink enough fluid: Drinking at least 12 cups of fluid--preferably water--a day is the most basic way to prevent kidney stones. The fluid dilutes the urine and decreases the risk for crystal formation.

• Limit meat intake: Consuming more than 6 to 8 ounces of meat daily can increase calcium and uric acid in the urine, increasing the acidity of urine and reducing the chemicals that inhibit crystal formation.

• Get adequate calcium: Meeting daily calcium intake recommendations based on age reduces the risk for kidney stone development, probably because calcium binds to oxalate in the gut, reducing oxalate levels in the urine.

• Avoid excess vitamin D: Often consumed with calcium to help absorption, vitamin D may raise the risk of developing calcium-based stones. Vitamin D has many health benefits, but for those at risk for kidney stones, limiting vitamin D consumption to age-specific recommended daily limits may be advised.

• Consider food choices: Limiting intake of oxalate-containing foods--such as spinach, beets, chocolate, peanuts, potatoes, and many other foods--is an important preventive strategy for those with calcium oxalate stones who also have conditions that affect the small bowel, such as Crohn's disease. For those who don't have digestive conditions or high urine oxalate levels, the benefits of diet changes are unclear. Because the diet is very difficult to follow, Mayo Clinic experts don't emphasize this strategy.

Source: Mayo Clinic Health Letter, 200 First St. S.W., Rochester, MN 55905, monthly, $27yr.
 

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