Kidney Stones

Description

Alternative Names

Risk Factors

Kidney stones are one of the most common disorders of the urinary tract, and are an ancient health problem. Evidence of this disorder was 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 prevalence has increased over the past three decades, perhaps because of increases in animal and dietary protein intake.

Gender and Age

Kidney stones affect about 12% of men and 5% of women by the time they are 70 years old.

Men. About 80% of kidney stone sufferers are men between the ages of 20 and 50 years. Caucasian men are at higher risk than other groups.

Women. Kidney stones that strike women are more apt to occur during pregnancy, usually in the late stages. During pregnancy, women tend to have a higher calcium intake and at the same time their kidneys handle calcium less efficiently. 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 and most are caused by excess calcium in the urine (hypercalciuria). Anatomic abnormalities 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.

Family History

People with a family history of kidney stones are at higher risk than those without relatives with stones. In one Italian analysis of kidney stone patients, 22% of their parents and 14% of their siblings also had one. Researchers are looking into markers or other factors that might predict the onset of stones in relatives, though 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, whereas 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. For example, studies report the highest occurrence of kidney stones in the southern region of the US and the lowest in the West.One study suggested that the higher risk may be due to a higher rate of hypertension in the South 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. Dietary calcium appears to be protective.

Weight Considerations. People who are overweight may be at higher risk than thinner people, although the evidence is weak. In a 2000 study, obesity was associated with abnormal blood and urine chemistries that appeared to increase the risk for stones in overweight women but not in overweight men. In any case, obesity poses particular difficulties in elimination of kidney stones. (It should be noted that fasting is associated with a higher risk for kidney stones, so anyone with risk factors for kidney stones and who wishes to lose weight should do so gradually.)

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 during stress. Among its other functions, vasopressin 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 favored. 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 results in a patient being immobilized or bedridden increases blood levels of calcium from bone breakdown, thereby posing a risk for stone formation.

Medical Conditions

Gout. A 2002 study reported that the prevalence of kidney stones in patients with gout was 13%. And, 2.7% of people with kidney stones had been diagnosed with gout, with the occurrence of gout being 8.6% in patients with two or more episodes of kidney stones. The study strongly suggests that the two disorders may share a common mechanism.

High Blood Pressure. Hypertensive people 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 hypertension, or if there is a mechanism common to both. Some experts suggest that imbalances between uric acid levels in the blood and urine and sodium excretion may put hypertensive patients at higher risk.

Bowel Diseases and Surgeries that Correct Them. Crohn's disease and ulcerative colitis (known as inflammatory bowel diseases) 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 are.

Surgeries that remove parts of the small intestine to correct bowel conditions pose a particular risk for short bowel syndrome. This is a major risk factor for both calcium oxalate and uric acid stones in these patients. People with Crohn's disease or intestinal infections and children with structural abnormalities in the small intestine are at risk for surgical procedures and short bowel syndrome.

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 it still remains high for some time after surgery.

Other Medical Conditions. Many other medical conditions, including but not limited to kidney disease, chronic diarrhea, certain cancers (e.g., leukemia and lymphomas), and sarcoidosis, put people at higher risk for stones.

Medications

Medications for AIDS. AIDS patients are at high risk for stones, mainly because of medications. Over 10% of AIDS patients who take indinavir develop stones, and the risk is even higher in AIDS patients who have hepatitis B or C or hemophilia, who are very thin, or who are receiving the antibiotic combination TMP-SMX. In one study of AIDS patients taking a combination of indinavir, zidovudine, and lamivudine, 36% developed kidney stones.

Other Drugs. Many drugs, including thyroid hormones and loop diuretics (drugs that increase urination), can increase calcium concentration in urine. Stones are an uncommon side effect of these medications, however. And, in fact, diuretics are also used to prevent calcium stones. Certain cancer chemotherapies can cause kidney stones. Taking medications for long periods that change the acidic content of urine, such as antacids, may increase susceptibility for kidney stones.