If you've ever passed a kidney stone, you do not want to repeat the experience! The sharp and irregular stones travel down the slender tube (ureter) leading from the kidney to the bladder, and from the bladder to the urethra, following the path by which urine exits the body. While tiny stones may pass unnoticed, a larger stone can induce some of the worst pain that humans experience.

Composition of Kidney Stones

Most kidney stones are composed of calcium and oxalic acid, substances present in the urine that can crystallize inside the kidneys. Although these chemicals occur in everyone's urine, our natural biochemistry is usually able to prevent them from crystallizing. However, sometimes these protective methods fail and a stone develops. This article focuses mainly on these "calcium oxalate stones."

Less commonly, kidney stones may be made from calcium and phosphate, from another substance called struvite (usually the result of an infection) or, rarely, from uric acid or cystine.

It isn't known why some people develop kidney stones and others do not. However, once you've had a stone, you are fairly likely to develop another.

Prevention

Low fluid intake greatly increases the risk of developing virtually all types of stones. For this reason, individuals at risk of developing stones are often advised to increase their fluid intake. However, while there is evidence that fluids in the form of coffee, tea, beer, and wine can decrease risk of kidney stone development, apple juice and grapefruit juice may have the opposite effect.

High intakes of sodium and protein (particularly animal protein) may also increase the risk of calcium oxalate stones, although some studies have found that protein has no such effect. Oxalate-rich foods such as spinach, rhubarb and cocoa may also increase the risk of developing calcium oxalate stones. Indirect evidence suggests that regular use of cranberry concentrate tablets might also increase risk of kidney stones. In addition, vitamin D affects calcium levels in the body, and prolonged use of extremely excessive doses of vitamin D has been known to cause kidney stones. Strangely, however, high-calcium foods don't seem to increase the risk of calcium oxalate stones.

Treating Kidney Stones

Conventional treatment for kidney stones varies depending on symptoms as well as the location and chemical composition of the stones. For those who pass a stone spontaneously, the main treatments are painkillers and fluids. The chemical composition of passed stones can be analyzed to determine their cause. Other stones may be detected earlier, when they are still in the kidney. Treatment depends on their location and symptoms. Those causing problems may be treated with "extracorporeal shock-wave lithotripsy," a technique that can break up these stones from outside the body, allowing them to pass more easily. Occasionally, however, surgery may be necessary.

"Silent" stones, or those causing no symptoms, are often treated with preventive measures alone. These methods include increasing fluids, modifying the diet, and taking drugs or supplements to alter the chemistry of the urine.