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Kidney & Ureteral Stone Risk Factors

For unknown reasons, the number of people in the United States with kidney stones has been increasing over the past 20 years. Caucasians are more prone to develop kidney stones than African Americans. Although stones occur more frequently in men, the number of women who get them has been increasing over the past 10 years, causing the ratio to change. If a person forms a stone, there is a 50 percent chance they will develop another stone.

Scientists do not always know what makes stones form. While certain foods may promote stones in susceptible people, researchers do not believe that eating specific items will cause stones in people who are not vulnerable. Yet factors such as a family or personal history of kidney stones and other urinary infections or diseases have a definite connection to this problem. Climate and water intake may also play a role in stone formation.

One of the main reasons stones forms is the loss of body fluids or being (dehydrated). When one does not consume enough fluids during the day, the urine can become concentrated and darker. This increases the chance that crystals can form from materials within the urine, because there is less fluid available to dissolve them. Stone formers should maintain 2 liters of urine output every day.  Also, a family history of stones, especially in a first-degree relatives (parent or sibling), dramatically increases the probability of having stones.

Diet can also affect the probability of stone formation. A high-protein diet can cause the acid content in the body to increase. This decreases the amount of urinary citrate, a "good" chemical that helps prevent stones. As a result, stones are more likely to form. A high-salt diet is another risk factor, as an increased amount of sodium passing into the urine can also pull calcium along with it. The net result is an increased calcium level in the urine, which increases the probability for stones. Intake of oxalate-rich foods such as leafy green vegetables, nuts, tea or chocolate may also worsen the situation.

Certain bowel conditions can also increase the risk such as chronic diarrhea, Crohn’s disease, and gastric bypass surgery. Obesity is also an independent risk factor for stone formation.

Although most stone formers do not have a medical condition that directly leads to their stone development, conditions do exist that place patients at high risk for stone formation. For example, stones can form because of obstruction to urinary passage like in prostate enlargement or stricture disease. Stone formation has also been linked to hyperarathyrodism, an endocrine disorder that results in more calcium in your urine. Susceptibility can also be raised if you are among the people with rare hereditary disorders such as cystinuria(formation of cystine stones in the kidneys, ureter, and bladder or primary hyperoxaluria (excessive urinary excretion of oxalate).  Development of kidney stones is due to the excess of the amino acid, cystine or the oxalate in your urine.

Another condition that can cause stones to form is absorptive hypercalciuria, a surplus of calcium in the urine that occurs when the body absorbs too much from food. Another condition that results in a high level of calcium in the urine is resorptive hypercalciuria where the kidney leaks calcium into the urine. The high levels result in calcium oxalate or phosphate crystals forming in the kidneys or urinary tract. Similarly, hyperuricosuria, excess uric acid tied to gout or the excessive consumption of protein-rich products, may also trigger kidney stones.

Consumption of calcium pills by a person who is at risk to form stones, certain diuretics or calcium-based antacids may increase the risk of forming stones by increasing the amount of calcium in the urine. Calcium oxalate stones may also form in people who have chronic inflammation of the bowel or who have had an intestinal bypass operation or ostomy. This is because of loss of more water from the body as well as absorption of oxalate from the intestine.

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Information provided by the American Urological Association.