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A number of risk factors are thought to create the conditions in which genetically susceptible people develop kidney stones.

Although passing larger kidney stones can be very painful, most kidney stones are passed without symptoms.

deCODEme calculates your genetic risk for developing kidney stones of the calcium type

Calcium stones are the most common types of kidney stones

There are different types of kidney stones, the most common of which are calcium stones. Other types of kidney stones are uric acid stones, struvite stones and cystine stones:

• Calcium stones are formed by a build-up of calcium, usually in the form of calcium oxalate. These stones account for 75 to 85 percent of all kidney stones and are more likely to occur in men. Oxalate is found in some fruits and vegetables, but the liver produces most of the body’s oxalate supply. High doses of vitamin D, and other dietary factors including intestinal bypass surgery and several different metabolic disorders, can increase the concentration of calcium or oxalate in urine.
• Uric acid stones are formed by a build-up of uric acid, a byproduct of protein metabolism. Uric acid stones account for 5 to 10 percent of all kidney stones and are more likely to occur in men, but also in individuals who are on high-protein diets.
• Struvite stones are formed by a build-up of calcium, magnesium and ammonium phosphate. Struvite stones account for 10 to 15 percent of all kidney stones, are mainly found in women, and are almost always the result of urinary tract infections.
• Cystine stones are the rarest form of kidney stones, accounting for only about 1 percent of all kidney stones. They are found in persons suffering from a hereditary disorder called cystinuria. Cystinuria is caused by excessive levels of an amino acid called cystine in the urine. Cystine stones occur in both men and women equally.

Scientists at deCODE genetics have found a common genetic variant in the CLDN14 gene on chromosome 21 that is associated with an increased concentration of urinary calcium and risk of developing kidney stones of the calcium type. The deCODEme Complete Genetic Scan identifies this variant (rs219778)in the CLDN14 gene and provides an interpretation of the risk for developing kidney stones in individuals of European descent.

Symptoms

Many kidney stones are passed without symptoms

Kidney stones sometimes remain in the kidneys unnoticed and many remain small enough to pass through the urinary tract without causing any symptoms. However, if kidney stones grow to a sufficient size before passing, they can lodge temporarily in the ureter (the tube between the kidney and the bladder). The resulting obstruction can lead to dilation and stretching of the upper ureter and spasms of the ureter muscle when trying to move the stone. This may cause severe episodic pain in the side and back (called renal colic) with nausea and vomiting, in addition to hematuria (blood in the urine), caused by damage to the inner lining of the urinary tract.

Passing larger kidney stones can be very painful

Although painful, kidney stones usually cause no permanent damage, and the symptoms are alleviated when the stones have passed. However, if a kidney stone gets stuck in the ureter on its way from the kidney to the bladder, severe unrelenting pain can occur until the stone is removed. In a minority of people the stone never makes its way out of the kidney, but continues to grow until it starts to interfere with the function of the kidney.

Risk Factors

A number of risk factors are thought to create the conditions in which genetically susceptible people develop kidney stones

The following factors, often in combination, may increase risk of developing kidney stones:

• Age and sex. Most people who develop kidney stones are between 20 and 70 years of age. The risk increases with age for most types of stones and men are in general more likely to develop kidney stones than women.
• Family or personal history. People with close relatives who have had kidney stones are more likely to develop them too. Those who have already had one or more kidney stones have a 50% risk of developing another.
• Lack of fluids. Inadequate fluid intake, will cause higher concentrations of substances in the urine that can lead to kidney stone formation in susceptible individuals. People in hot, dry climates or those who exercise strenuously without replacing lost fluids, have been found to be at increased risk of developing kidney stones.
• High blood pressure. Having high blood pressure has been found to double the risk of forming kidney stones.
• Diet. People on high-protein, high-calcium, high-sodium, and low-fiber diets are at increased risk of developing kidney stones. There is also evidence that certain medications, such as aspirin, antacids, calcium and vitamin D supplements, may increase risk of developing a kidney stone.
• Obesity. High body mass index (BMI), increased waist circumference, and weight gain have been linked to kidney stones in long-term studies of large populations. The relationship is stronger in women than in men. Although obesity is also a risk factor for gallstones they are not related to kidney stones in any way.
• Limited activity. People who are very sedentary or bedridden for a long period of time are at increased risk of developing kidney stones. This may be due to the fact that limited activity can cause your bones to release more calcium, increasing the calcium excreted into the urine.
• Changes in the digestive system, such as gastric bypass surgery, inflammatory bowel disease or chronic diarrhea affect the absorption of calcium and can increase the levels of stone-forming substances in urine.

Prevention and Treatment

Preventing kidney stones involves lifestyle changes

People who know they are at an increased risk of developing kidney stones may be able to prevent them by following specific recommendations from their doctors. These recommendations mostly involve lifestyle changes, aimed at the recognized risk factors, such as getting enough fluids, adhering to a recommended diet, and adequately managing body-weight, and hypertension.

If these measures are not effective and blood and urine tests reveal a correctable chemical imbalance or indicate that an already identified asymptomatic kidney stone is growing in size, the doctor may prescribe certain medications.

Treatment of kidney stones

In terms of treatment, about 90 percent of kidney stones will pass by themselves within three to six weeks, and are only treated with watchful waiting and pain medications. When kidney stones are associated with an infection, a severe obstruction, or affect kidney function, removal of the stone however becomes necessary.

Several different methods are available that depend on the size, location and type of stone. Certain types of stones can sometimes be dissolved using medications. However, the most common type of kidney stones (the calcium-containing stones) cannot be dissolved. Stones that cannot be dissolved are removed by passing a telescopic instrument into the bladder or into the ureters to pull the stones out or to break them into small fragments with shock waves or laser beam. In certain cases, a telescopic instrument is inserted directly into the kidney through a small slit made in the patient’s side to pull the stone out whole or break it down into small fragments that can more easily be passed.

This content was last reviewed on February 09, 2010.

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