Nearly 12 percent of men and 5 percent of women in the United States will feel a kidney stone during their life—and it's not pleasant. Although they're often described as "the worst pain I've ever experienced," kidney stones rarely cause long-term damage. Kidney stones can occur at any age, but men are more likely to develop stones between the ages of 40 and 70, while women are more likely to develop a kidney stone in their 50s. Often kidney stones are a recurring problem; having had one kidney stone puts you at increased risk for a second.
Medically known as urolithiasis or nephrolithiasis, kidney stones can form anywhere along the urinary tract, including the kidneys, bladder, ureter, or urethra. A kidney stone starts as a microscopic crystal. Over time, the crystal enlarges or multiple crystals can aggregate to form a single large kidney stone. Pain develops when the stone breaks away and becomes lodged in the urinary tract, either partially or totally blocking the passage of urine. Other common names for a kidney stone include renal calculus, renal stone, ureteral calculus or stone, bladder calculus, or urethral stone. Kidney stones are totally unrelated to gallstones, which form in the gallbladder.
When a stone is in the kidneys, many people are totally unaware of its presence. These stones are often incidentally discovered on an X-ray or other imaging technique performed for an unrelated medical issue. If shape and size permit, kidney stones sometimes pass without significant discomfort after they break loose. However, even a small stone can wreak havoc as it moves down the urinary tract.
Each year nearly 3.3 million Americans seek out medical care for kidney stone removal and pain relief at a cost of about $5.3 billion per year. Treatment strategies include waiting for the stone to pass, physically breaking the stone into fragments, or surgically removing it; often some combination of the three approaches is required. Since people who have had one kidney stone are likely to develop more, kidney stone treatment involves not only addressing the immediate problem but also learning how to prevent formation of additional kidney stones.
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The urinary tract includes the kidneys, ureter, bladder, and the urethra. Urine is produced in the kidneys, two bean-shaped organs the size of your fist located in the lower back, flanking the spine. The kidneys release urine into the ureter, a small muscular tube that can dilate up to 7 millimeters in diameter (about 1/4 of an inch) and connects the kidney to the bladder where urine is stored. When the bladder is full, we release the urine into a narrow tube, the urethra, which channels the urine out of the body.
Each day, nearly one quarter of the blood that's pumped by the heart flows through the kidneys into a network of tiny blood vessels that filter the blood. Together the kidneys contain 1 million tiny structures called nephrons that filter this blood, directing the waste products into tubules. In the tubules the wastes are further processed and partially reabsorbed to generate roughly 1 to 3 quarts of urine that the body needs to eliminate each day. The waste products in the blood are derived from the foods we eat and the normal breakdown of tissue in the body. Not only do the kidneys keep the blood chemically balanced by converting waste products into urine and discharging excess water, but they also produce hormones that are needed to stimulate bone marrow to make red blood cells (erythropoietin), regulate blood pressure (renin), and help maintain healthy calcium levels in the bones and body (calcitriol).
In general, kidney stones form when specific compounds in the urine become overly concentrated, causing minerals to crystallize. This usually happens near the end of tubules, before fluid leaves the kidney. Initially, the crystals are the size of tiny grains of sand, but over time they can aggregate to form a pebble about a half inch in diameter up to the size of a golf ball. Stones can be relatively smooth and round or irregularly shaped, like an antler. There are four main types of kidney stones, each of which is associated with different chemical conditions in the urinary tract.
The risk factors for kidney stones fall into two categories: those you can control through lifestyle choices and those traits you are born with. Having a risk factor doesn't mean that you'll develop a disease or condition. Medical research continues to reveal how risk factors interact to influence a person's health and life span. However, understanding your risk allows you to balance the value you place on your health with the risk that may compromise your health in the future. In the United States, the incidence of kidney stones is on the rise, especially in young children. Many experts attribute this increase to changes in lifestyle such as poor diet and a decrease in water consumption.
Risk factors for forming a kidney stone include:
Last reviewed on 10/13/09
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