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Kidney stones

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of kidney stones.

Alternative Names

Calcium stones; Nephrolithiasis

Risk Factors

Kidney stones are one of the most common disorders of the urinary tract. They are an ancient health problem. Evidence of kidney stones has been found in an Egyptian mummy estimated to be more than 7,000 years old.

An estimated 1.3 million Americans seek medical help for kidney stones each year. At this time, studies suggest kidney stones affect over 5% of Americans and that the rate has increased since the 1970s, perhaps because of increases in animal and dietary protein intake.

Gender and Age

Men. The risk of kidney stones increases in a man's 40s and continues to rise until age 70. Caucasian men are at higher risk than other groups.

Women. The risk of kidney stones peaks in a woman's 50s. In younger women, stones are more likely to develop during the late stages of pregnancy. Pregnant women tend to have a higher calcium intake, but their kidneys do no handle the calcium as well as they did prior to pregnancy. Kidney stones are still a rare occurrence during pregnancy, however, affecting only 1 in 1,500 pregnancies.

Risk Factors in Children. Stones in the urinary tract in children are usually due to genetic factors. Most of the time, the cause is excess calcium in the urine (hypercalciuria). Deformities in the urinary tract pose a significant risk for kidney stones in children. Children with low birth weight who need to be fed intravenously are also at risk for stones.

Obesity and Weight Gain

Obesity and weight gain are both associated with an increased risk of kidney stones.

• Men who weigh more than 220 lbs are 44% more likely to develop kidney stones than men who weigh less than 150 lbs.
• Women who are obese are 90% more likely to develop kidney stones than women with a lower body mass index (BMI).

Higher BMIs and larger waist circumferences are both risk factors for kidney stones. Researchers think that there may be a link between fat tissue, insulin resistance, and urine composition. People with larger body sizes may excrete more calcium and uric acid, which increase the risk of kidney stone formation.

Family History

A family history of kidney stones increases one's risk for the condition. Researchers are looking into markers or other factors that might predict the onset of stones in relatives, although none has yet been clearly identified. One report found that among the siblings of patients with calcium stones, sisters with higher urinary calcium levels and more acidic urine were more likely to develop stones. Brothers with high urinary calcium, low urinary potassium, and older age were more likely to have the problem. A family history of gout may also predispose a person to stones.

Ethnicity

According to a 2003 study of American ethnic groups, Caucasians have the highest incidence of kidney stones (5.9%) followed by Mexican Americans (2.6%). African Americans have the lowest risk (1.7%).

Geographic Differences

Dietary factors, minerals in local water, or both may contribute to geographic differences that have been observed in the prevalence of kidney stones. Studies have reported the highest occurrence of kidney stones in the southern region of the United States and the lowest in the west. One study suggested that the higher risk may be due to a higher rate of hypertension in the southern states and certain dietary habits, particularly lower intake of magnesium and low use of calcium supplements. Higher rates of kidney stones have been reported in areas of Australia where magnesium levels in drinking water are low. Hard water tends to have higher amounts of protective calcium and magnesium, although evidence suggests that the hardness or softness of water does not significantly affect risk.

Life Style Factors

Specific Foods . In general, certain foods increase the risk for stones only in people who have genetic or medical susceptibility. People whose diets are high in animal protein and low in fiber and fluids may be at higher risk for stones. A number of foods contain oxalic acid, but there is no proof that such foods make any major contribution to calcium oxalate stones in people without other risk factors. However, several studies have shown that increasing dietary calcium and restricting salt, animal protein, and foods rich in oxalate can help prevent calcium oxalate stones from returning.

Stress. One study reported that people who had a major, stressful life experience were more likely to develop stones than those who had not. Some experts speculate that this increased risk may be due to a hormone called vasopressin, which is released in response to stress. Vasopressin also increases the concentration of urine.

Sleep Position. Sleeping in the same position consistently may influence risk. A 2001 study reported that in people who had a history of kidney stones, recurrences tended to occur on the same side that people slept on. An earlier study suggested that people who had kidney stones were more apt to sleep on their stomachs. Movement during sleep did not appear to affect the risk.

Being Bedridden. Any medical or physical condition that keeps a person in bed or immobile increases blood levels of calcium from bone breakdown, thereby posing a risk for stone formation.

Medical Conditions

Gout. A 2002 study reported that the rate of kidney stones in patients with gout was 13%. The study strongly suggests that the two disorders may share a common action.

High Blood Pressure.  Persons with high blood pressure are up to three times more likely to develop kidney stones. It is not entirely clear whether having high blood pressure increases the risk for a stone, whether stones lead to high blood pressure, or if there is an action linking both. Some experts suggest that imbalances between uric acid levels in the blood and urine and sodium excretion may put patients with high blood pressure at higher risk.

Inflammatory Bowel Disease. Crohn's disease and ulcerative colitis cause problems in intestinal absorption that significantly increase the risk for kidney stones. Men with these conditions may be at higher risk for stones than women.

Urinary Tract Infections (UTIs). Struvite stones are almost always caused by urinary tract infections.

Hyperparathyroidism. Some people with hyperparathyroidism develop kidney stones. Surgery to remove the parathyroid gland in such patients reduces the risk for stone formation, but the risk still remains high for some time after surgery.

Other Medical Conditions. Kidney disease, chronic diarrhea, certain cancers (e.g., leukemia and lymphomas), and sarcoidosis put people at higher risk for stones.

Medications

AIDS medications.  Over 10% of persons with AIDS who take the medicine indinavir develop stones. The risk is even higher in patients with AIDS who also have hepatitis B, hepatitis C, or hemophilia, as well as those who are very thin or who take the antibiotic combination TMP-SMX. In one study of persons with AIDS who took a combination of indinavir, zidovudine, and lamivudine, 36% developed kidney stones.

Other Drugs. Kidney stones are a rare side effect of thyroid hormones and loop diuretics (drugs that increase urination). In fact, diuretics are also used to prevent calcium stones. Certain cancer chemotherapies can also cause kidney stones. Taking medicines for long periods that change the acidic content of urine, such as antacids, may increase susceptibility for kidney stones.

• Review Date: 5/22/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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