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An in-depth report on the causes, diagnosis, treatment, and prevention of kidney stones.
Calcium stones; Nephrolithiasis
An assessment of diet and over-the-counter vitamins and supplements can be useful in determining nutritional recommendations that may be helpful in preventing kidney stones from recurring.
Preventive drug therapy is matched to the exact type of stone formation. For some types of stones, this can be highly effective with a success rate of over 80%.
Kidney stones are hard, solid particles that form in the urinary tract. In many cases, the stones are very small and can pass out of the body without any problems. However, if a stone (even a small one) blocks the flow of urine, excruciating pain may result, and prompt medical treatment may be needed.
Urine is formed in the kidneys. The two kidneys are located deep behind the abdominal organs, below the ribs and toward the middle of the back. The kidneys filter out fluids and waste from the body, producing urine. As the urine passes through the kidneys, it becomes more concentrated. From the kidneys, urine flows through thin tubes called ureters into the bladder. The bladder's stretchy walls expand to store the incoming urine until it leaves the body through a tube called the urethra.
The two kidneys are located deep behind the abdominal organs, below the ribs and toward the middle of the back.
The kidneys are responsible for removing wastes from the body, regulating electrolyte balance and blood pressure, and stimulating red blood cell production.
Occasionally, high levels of chemicals in the urine form into crystals. Eventually these crystals become large enough to form stones in the kidney, a condition called nephrolithiasis. Stones (calculi) may also form in the ureter or the bladder. Combinations of minerals and other chemicals that can come from a person's diet, make up the salts in these stones.
Calcium Stones: About 80% of all kidney stones contain calcium, usually combined with oxalate, or oxalic acid. Many common vegetables, fruits, and grains contain oxalate.
A smaller percentage of calcium stones are made of calcium phosphate (called brushite).
Uric Acid Stones: Uric acid is responsible for almost 10% of kidney stones. It is the breakdown product of purines, nitrogen-containing compounds found in the body and in certain foods. Uric acid enters the bloodstream, and then passes primarily into the kidneys. From the kidneys, uric acid leaves the body in the urine. Often, uric acid stones occur with calcium stones.
Struvite Stones: Struvite stones are made of magnesium ammonium phosphate. They are almost always associated with certain urinary tract infections. Worldwide, they account for up to 30% of all kidney stones. In the United States, however, fewer than 15% of all stones are struvite. Most struvite stones occur in women. The rate of these stones may be declining in America, perhaps because of better control of urinary tract infections.
Cystine Stones: A buildup of the amino acid cystine, a building block of protein, causes 1% of kidney stones in adults and up to 8% of stones in children. The tendency to form these stones is inherited. Cystine stones grow rapidly and tend to recur. If not treated promptly, they can eventually lead to kidney failure.
Xanthine Stones: Other kidney stones are composed of xanthine, a nitrogen-containing compound. These stones are extremely uncommon and usually occur as a result of a rare genetic disorder.
The key process in the development of kidney stones is supersaturation.
Different factors may reduce the volume of urine, or increase the amount of chemicals.
Deficiencies in Protective Factors: Normally, urine contains substances that protect against stone formation, including:
These substances carry out the following protective actions:
Not having enough of these protective substances can cause stones.
Changes in Urine Acidity: The acidity of urine is indicated by the pH scale in which a pH value of 7.0 is neutral, a low pH (below 7.0) is acidic, and a high pH (above 7.0) is alkaline. The normal pH range of urine is 4.6 to 8.0. Changes in the acid balance of the urine can affect stone formation.
Often, the cause of calcium stones is not known and is referred as idiopathic (of unkno0wn cause) nephrolithiasis. Research suggests that nearly all stones result from problems in the breakdown and absorption of calcium and oxalate. Genetic factors may play a role in about half of these cases. Many medical conditions and drugs can also affect digestion and intestinal absorption.
Excess Calcium in the Urine (Hypercalciuria): Hypercalciuria is a condition in which there is too much calcium in the urine. It is responsible for as many as 70% of calcium-containing stones. A number of conditions may produce hypercalciuria. Many are due to genetic factors, but most cases are due to unknown causes (idiopathic).
The following can lead to hypercalciuria and calcium stones:
Excess Oxalate in the Urine (Hyperoxaluria): Oxalate is the most common stone-forming compound. Too much oxalate in the urine is responsible for up to 60% of calcium stones and is a more common cause of stones than excess calcium in the urine.
Hyperoxaluria can be either a primary or secondary condition.
Secondary hyperoxaluria is usually caused by too much dietary oxalates (found in a number of common vegetables, fruits, and grains) or by problems in the body's breakdown of oxalates. Such defects may be due to various factors:
Female hormones (estrogens) actually lower the risk of hyperoxaluria. Estrogen may help prevent the formation of calcium oxalate stones by keeping urine alkaline, and by raising protective citrate levels.
People who undergo the most common type of gastric bypass surgery, the Roux-en-Y, may be at increased risk for calcium oxalate kidney stones beginning 6 months after surgery. The added kidney stone risk is thought to be due to changes in the urine. People who have undergone Roux-en-Y gastric bypass surgery have excess oxalate and low levels of citrate in their urine after the procedure.
Gastric banding, another type of weight loss surgery, does not seem to increase the risk for kidney stones.
Excessive Calcium in the Bloodstream (Hypercalcemia): Hypercalcemia generally occurs when bones break down and release too much calcium into the bloodstream. This is a process called resorption. It can result from several different diseases and events, including:
High Levels of Uric Acid in the Urine (Hyperuricosuria): Hyperuricosuria is excess uric acid in the urine. Occurs in 15 to 20% of people (mostly men) with calcium oxalate stones. Urate, the salt formed from uric acid, creates the center of a crystal (nidus), around which calcium oxalate crystals form and grow. Such stones tend to be severe and recurrent. They appear to be strongly related to a high intake of protein. (Hyperuricosuria also plays a major role in some uric acid stones.)
Low Urine Levels of Citrate (Hypocitraturia): Citrate is the main substance in the body that is responsible for removing excess calcium. It also blocks the process that turns calcium crystals into stones. Low levels of citrate in the urine is a significant risk factor for calcium stones. Hypocitraturia also increases the risk for uric acid stones. This condition most likely contributes to about a third of all kidney stones.
Many conditions can reduce citrate levels, including:
Low Levels of Other Stone-Blocking Compounds: Several other compounds in the urine, including magnesium and pyrophosphate, also prevent the formation of calcium stones. If any of these compounds are lacking, stones may develop.
Human body tissues, and certain foods, contain compounds called purines. Purine-containing foods include dried beans, peas, and liver. When the body breaks down purines, it produces uric acid. The presence of a certain level of uric acid in the body is normal, but excess uric acid can lead to stones.
The following conditions are usually seen in patients with uric acid stones:
Note: Hyperuricosuria can also trigger calcium stones. Therefore, people with hyperuricosuria may have a combination of calcium and uric acid stones.
Many conditions and other factors may contribute to, or cause, uric acid stones:
Other risk factors include:
Struvite stones are almost always caused by urinary tract infections. Bacteria produce certain enzymes, which raise the concentration of ammonia in the urine. Ammonia makes up the crystals that form struvite stones. The stone-promoting bacteria are usually Proteus, but they may also include Pseudomonas, Klebsiella, Providencia, Serratia, and Staphylococcus. Women are twice as likely to have struvite stones as men.
Other stones, including cystine and xanthine stones, are usually due to genetic abnormalities.
Causes of Cystine Stones: Cystine stones develop from genetic defects that cause the abnormal transport of amino acids in the kidney and gastrointestinal system, leading to a buildup of cystine. Researchers have identified two genes responsible for this condition, which are SLC3A1 and CLC7A9.
Causes of Xanthine Stones: In some cases, xanthine stones may develop in people being treated with allopurinol for gout.
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.
Kidney stones affect more than 8% of Americans, and the rate has increased since the 1970s. People who form kidney stones appear to be at increased risk for certain other disorders, including heart attacks.
Not drinking enough water can increase the risk of developing a kidney stone. The amount of fluids you need can depend on the climate you live in, your activity level, and any history of kidney stones.
Men: Kidney stones are two times more common in men than women, but the likelihood of stones is increasing in both men and women. The risk of kidney stones increases in men in their 40s and continues to rise until age 70. By age 70, 11% of men will have had a kidney stone that causes symptoms. Caucasian men have a higher risk than other ethnic 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 not handle the calcium as well as they did before pregnancy. Pregnant women tend to form calcium phosphate stones. Kidney stones are still rare 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 too much calcium in the urine (hypercalciuria). Deformities in the urinary tract pose a significant risk for kidney stones in children. Babies born at a low birth weight who need to be fed intravenously are also at risk for stones.
Rates of kidney stones in adolescents have doubled in the last 25 years. Although researchers do not know the exact reason for this increase, they think it may have to do with body weight, diabetes and hypertension, which have been rising in young people over the years.
Obesity and weight gain are both associated with an increased risk for kidney stones.
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, dehydration, and urine composition. People with larger body sizes may excrete more calcium and uric acid into the urine, which increases the risk for kidney stone formation.
Having a family history of kidney stones doubles a person's risk for the condition. Researchers are looking into genetic markers or other factors that might predict the risk of kidney stones in relatives, although none has yet been clearly identified. A family history of gout may also make a person more vulnerable to developing stones.
Caucasians seem to have the highest incidence of kidney stones, followed by Mexican Americans. African-Americans have the lowest risk. Caucasians are three times more likely to form kidney stones than African-Americans. However, dietary factors can diminish any protective effects of ethnicity.
Dietary factors, minerals in local water, or both may contribute to geographic differences that have been observed in the occurrence of kidney stones. Studies have reported the highest occurrence of kidney stones in the southern region of the United States and the lowest occurrence in the western region.
Specific Foods: In general, certain foods increase the risk for stones, but only in people who have a genetic or medical vulnerability. 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 who do not have 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.
Eating a high-calcium diet does not appear to increase the risk for kidney stones, as long as the diet also contains plenty of fluids, potassium, and phosphate. (Increasing calcium alone may pose a modest risk for stones.)
Calcium supplements on the other hand have been associated with an increased risk of kidney stones in several studies. For example, the Women's Health Initiative showed that postmenopausal women who took 1,000 mg calcium/400 I.U. vitamin D supplements daily had a 17% higher risk of kidney stones. Calcium from food sources appears to be the best option.
Stress: People who have had a major, stressful life experience may be more likely to develop stones. Some experts speculate that this increased risk may be due to a hormone called vasopressin, which is released in response to stress. Vasopressin also decreases the volume of urine, which makes the chemicals in urine more concentrated and prone to forming crystals and stones.
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.
Diabetes: People with type 2 diabetes are at increased risk for developing kidney stones, particularly uric acid stones.
Gout: People with gout are at high risk for uric acid stones.
High Blood Pressure: People 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, or if stones lead to high blood pressure, or if there is a factor linking both conditions.
Inflammatory Bowel Disease (IBD): Crohn disease and ulcerative colitis cause problems in the absorption of substances in the intestines. These problems significantly increase the risk for kidney stones, particularly in men.
Urinary Tract Infections (UTIs): UTIs are almost always the cause of struvite stones.
Hyperparathyroidism: The parathyroid glands regulate calcium levels in the body through parathyroid hormone. In hyperparathyroidism, one or more of these glands makes too much parathyroid hormone. Some people with hyperparathyroidism develop kidney stones. Surgery to remove the hyperactive 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, other GI conditions such as celiac disease or surgery in the intestines, certain cancers (such as leukemia and lymphoma), and sarcoidosis (a type of inflammation in lymph nodes and other tissues) put people at higher risk for stones.
Uricosuric Medications: Uricosuric agents are used to treat gout by lowering uric acid levels in the blood. As a result, higher levels of uric acid end up in the urine (hyperuricosuria), and can lead to an increased risk for kidney stones. These agents should not be used for individuals who already have hyperuricosuria.
AIDS medications: More than 10% of AIDS patients who take the medicine indinavir develop stones. The risk is even higher in people 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 of trimethoprim/sulfamethoxazole (TMP-SMX).
Other Drugs: Kidney stones are a rare side effect of thyroid hormones and loop diuretics (drugs that increase urination), although diuretics are also used to prevent calcium stones. Certain cancer chemotherapy drugs can also cause kidney stones. Long-term use of medications such as calcium-based antacids, which change the acid content of urine, may increase the risk for kidney stones.
Ephedrine (found in some drugs used to treat asthma and congestion), triamterene (sometimes used to treat high blood pressure and fluid build-up), magnesium antacids (silicates), TMP-SMX (used to treat certain infections), topiramate (used to treat certain seizures), carbonic anhydrase inhibitors (used to treat glaucoma), furosemide (used to treat high blood pressure or fluid retention), vitamin C or D excess, and overusing laxatives may also promote the formation of kidney stones.
Certain antibiotics and drug therapies for type 2 diabetes are also associated with kidney stone formation.
In many cases, kidney stones do not produce symptoms. However, if a stone becomes trapped (or lodged) in the ureter (the thin tube between the bladder and kidney), symptoms can be very severe. Often, symptoms vary depending on the stone's location and its progress.
Kidney stone attacks tend to be most common late at night or in the early morning, possibly because of low urine output during these times.
The size of the stone does not necessarily predict the severity of the pain. A very tiny crystal with sharp edges can cause intense pain, while a larger round stone may not be as distressing. Struvite stones can often occur without symptoms.
The doctor will perform a physical exam. This includes tapping on the back over the kidneys and pressing on the abdomen to detect tender locations.
The person's age is a significant factor in the diagnosis. Kidney stones that occur in children and young people are more likely to result from inherited problems that cause excess cystine, xanthine, or, in some cases, calcium oxalate. In adult people, calcium stones are most common.
A medical history may help predict which crystal has formed the stone. The doctor will need to know the following:
Many conditions can cause symptoms similar to those of kidney stones. Usually the diagnosis is easily made because of the type of symptoms, but it is not always clear. Urinary tract infections can cause similar, but usually less intense, pain. In fact, people with an infection may also have a kidney stone.
Other causes of pain that may mimic kidney stones include:
Various imaging techniques are helpful in determining the presence of kidney stones. The best approach uses spiral (or helical) computed tomography (CT) scans. If these scans are not available, the person will need an ultrasound or standard x-rays. If no stones show up, but the person has severe pain that suggests the presence of kidney stones, the next step is an intravenous pyelogram (IVP).
X-Rays: A standard x-ray of the kidneys, ureters, and bladder may be a good first step for identifying stones, because many stones are visible on x-rays. Calcium stones can be identified on x-rays by their white color. Cystine crystals can also show up on x-rays.
Computed Tomography (CT): CT scans use x-rays with computer technology to produce 3D images of the body. A type of CT scan called a spiral or helical CT scan is currently the best method for diagnosing stones in either the kidneys or the ureters. CT scans can be used to find the exact location of the stone, as well as to look for anatomical problems that may have led to stone formation. This test is fast, noninvasive, and it provides detailed, accurate images of even very small stones. If stones are not present, a spiral CT scan can often identify other causes of pain in the kidney area. It is better than x-rays, ultrasound, and IVP for detecting kidney stones. Experts hope spiral CT will eventually be able to identify the chemicals present in a stone.
Ultrasound: Ultrasound is a noninvasive technique that uses sound waves to create images of internal organs and structures. Ultrasound can detect uric acid stones and blockages in the urinary tract. It is not useful for finding very small stones, but some research indicates that it may be an effective first diagnostic step in the emergency room to help identify whether a person has a stone. Ultrasound is also effective in children.
Intravenous Pyelogram (IVP): With IVP, the doctor injects a special dye into the person's vein. A technician then takes x-rays as the dye enters the kidneys and travels down the urinary tract. The dye helps visualize any abnormalities in the urinary system. IVP is invasive but, until recently, it was the most cost-effective method for detecting stones. Where it is available, spiral CT is now preferred, since it gives a faster diagnosis and is more accurate, safer, and similar in cost.
IVP should not be used on patients with kidney failure. There is also a risk for an allergic reaction to standard dyes, although newer, less allergenic dyes are becoming available.
In the procedure intravenous pyelogram (IVP), the person is injected with dye. X-rays are taken as the dye travels through the urinary tract. This procedure is done to confirm the presence of kidney stones, although some stones may be too small to see.
Magnetic Resonance Imaging (MRI): MRI uses powerful magnets and radiowaves to provide detailed images of internal organs and tissues. MRI techniques are showing promise for diagnosing urinary tract obstruction, but they do not yet accurately reveal small stones, or stones that do not cause a blockage. Because no radiation is involved with MRIs and ultrasounds, they are good options for children and pregnant women.
Urine samples are needed to evaluate features of the urine, including its acidity and the presence of:
Clean-Catch Urine Sample for Culturing: After determining that a kidney stone is present, the health care provider usually gives the patient a collection kit, including filters, to try to catch the stone or gravel as it passes out. The type of crystals that make up the stone can be determined (crystallography). The urine may also be tested (cultured) for the presence of infection-causing organisms. A clean-catch urine sample is almost always required for culturing. To provide a clean catch, do the following:
Twenty-Four Hour Urine Collection: A 24-hour urine collection may be needed to measure urine volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate, and creatinine.
Testing Urine Acidity: Testing whether urine is acidic or alkaline helps to identify the specific type of stone. The levels of acidity or alkalinity in any solution, including urine, are indicated by the pH scale:
Urine tests that are used to determine the specific chemical and biological factors causing the stone should be performed about 6 weeks after the attack, since the attack itself may change the levels of such substances, including calcium, phosphate, and citrate.
Note that calcium levels in the urine may be abnormal even in many people who do not have stones. In addition, high urinary concentrations of calcium may pose a greater or lesser risk for stones, depending on a person's age.
A dipstick test for blood in the urine (called hematuria) is typically performed when people come to the emergency room with flank pain (the primary symptom of kidney stones). About a third of people with kidney stones do not show blood in the urine, so other tests may be needed.
Blood Tests for Stone Factors: Blood and urine tests help determine what substances formed the crystals. This allows the doctor to determine the appropriate treatment and preventive measures.
Blood tests may help determine blood levels of urea nitrogen, creatinine, calcium, phosphate, and uric acid in people with known or suspected calcium oxalate stones. Doctors will usually schedule these tests about 6 weeks after the attack, in order to measure these substances when the stone has been passed and the patient has been stabilized. This is particularly true in people with recurrent stones.
Parathyroid Tests: Tests to detect parathyroid hormone levels are given if the doctor suspects hyperparathyroidism based on other signs and symptoms.
Tests for Infection: A test result that shows a high white blood cell count might indicate infection. Such results, however, could be misleading, since the number of white blood cells could also increase in response to the extreme physical stress of a kidney stone attack.
Tests for Metabolic Problems: About half of children with stones have an identifiable metabolic disorder, which increases their risk of stone recurrence five-fold. Experts argue whether tests for metabolic disorders are routinely needed once the stone composition has been determined. Studies suggest the following:
Kidney stones that are removed are sent for stone analysis (crystallography).
When tests show someone has a kidney stone, the next step is to determine treatment. People who have severe pain, vomiting, fever, or symptoms of infection should be evaluated and treated in the emergency room. The size, location, type, and number of stones are important factors in determining the best treatment.
Strong opioid painkillers are often required for a severe kidney stone attack. However, doctors will usually not give such drugs until they confirm the presence of a kidney stone with an imaging study.
In about 85% of people, the kidney stones are small enough (about 5 mm) that they pass through normal urination, usually within 2 to 3 days. In some cases, a stone may take weeks to months to pass, although the pain usually goes away before that.
The person should drink plenty of water (2 to 3 quarts a day) to help move the stone along, and take painkillers as needed. The doctor usually provides a collection kit with a filter and asks the patient to save any passed stones for testing.
If the stone has not passed in 2 to 3 days, the patient will need additional treatments. In some severe cases, hospitalization may be necessary.
Alpha blockers (such as tamsulosin) can relax muscles in the urinary tract, helping kidney stones pass.
Diuretics: Diuretics are medicines commonly used to treat high blood pressure and other disorders. They remove fluid and sodium from the body. Low doses of a class of diuretics, known as thiazides, are sometimes used to reduce the amount of calcium the kidneys release into the urine, thereby reducing recurrent calcium stone formation. Thiazides include:
However, thiazides also cause potassium loss, which reduces citrate levels and can increase the risk for stones. People taking thiazide pills may also take potassium citrate to prevent citrate loss. Amiloride (Midamor) is a potassium-sparing diuretic, which may be used if a thiazide does not work. Thiazides may cause muscle cramps. Researchers are looking at lower dosing options for thiazides.
Citrates: Citrate salts are often given to people with calcium oxalate or uric acid stones:
Citrates may cause stomach upset. People with struvite stones, urinary tract infections, bleeding disorders, or kidney damage should not use these products. People who take citrate supplements containing potassium should not take any other medications that contain potassium or prevent its loss (such as potassium-sparing diuretics). People with peptic ulcers should avoid citrate supplements, or discuss using non-tablet forms with their doctors.
Phosphates: Phosphates help reduce the breakdown of bone that releases calcium into the bloodstream. They are also involved in the kidney's reabsorption of calcium from the urine.
Avoid acidic forms of phosphate, because they increase the risks for both hypocitraturia and hypercalciuria. They may cause gastrointestinal distress.
Cholestyramine (such as Questran and Questran Light): is a drug used to reduce cholesterol levels. However, because it binds with oxalate in the intestine, it is also used to reduce high oxalate levels in urine (hyperoxaluria). The drug usually comes in a powder that is dissolved in liquid. Bloating and constipation are common side effects of this drug. Cholestyramine also interferes with other medications, including digoxin (Lanoxin) and warfarin, and it may contribute to calcium loss and osteoporosis. In order to prevent such interactions, take other drugs 1 hour before, or 4 to 6 hours after taking cholestyramine.
Long-term use of cholestyramine may cause deficiencies of vitamins A, D, E, and K. Vitamin supplements may be necessary.
Sodium Bicarbonate: People who have uric acid stones from acidic urine may take sodium bicarbonate to reduce urine acidity. People taking sodium bicarbonate must test their urine regularly with pH paper, which turns different colors depending on whether the urine is acidic or alkaline. Too much sodium bicarbonate can cause the urine to become too alkaline. This increases the risk for calcium phosphate stones. People who need to reduce the amount of sodium they take in (as a result of other medical conditions) should not use sodium bicarbonate.
Potassium Citrate: Potassium citrate, which restores citrate to the urine, is useful for people with high levels of uric acid in the urine.
Allopurinol: Allopurinol (Lupurin, Zyloprim) is very effective at reducing high blood levels of uric acid, and it may be helpful for people with uric acid stones. Allopurinol will not prevent calcium stones from forming. There is also a slight risk for the formation of xanthine stones with this drug. Side effects include diarrhea, headache, muscle pain, and fever. About 2% of people have an allergic reaction to allopurinol that causes a rash. In rare cases, the rash can become severe and widespread enough to be life threatening.
Allopurinol reduces uric acid levels rapidly, so it may trigger an attack of gout in vulnerable people. To relieve this problem, people taking allopurinol should also take a nonsteroidal anti-inflammatory drug (NSAID) for 2 or 3 months. Aspirin should not be taken, because it increases uric acid levels. People should discuss the appropriate NSAID choice with their doctor.
In 2009, the U.S. Food and Drug Administration (FDA) approved febuxostat (Uloric) to treat gout. It is the first new treatment for gout in 40 years. Febuxostat lowers uric acid levels by inhibiting the same enzyme as allopurinol. People who are allergic to allopurinol can take febuxostat. This new drug is very effective, but expensive. Researchers continue to study the effectiveness of allopurinol compared to febuxostat in clinical trials.
Before people can receive any medical treatment for struvite stones, they must have have the stones removed with one of the techniques below.
Antibiotics for Eliminating Infection: People with struvite stones should receive ongoing treatment with antibiotics to keep the urine free of the bacteria that cause urinary tract infections. Careful follow-up and urine testing are extremely important. A high urine pH indicates low acidity and an increased risk for infection.
Acetohydroxamic Acid (AHA): AHA, or Lithostat, is beneficial when used with long-term antibiotics. AHA blocks enzymes that bacteria release, and it has been effective in preventing stones even when bacteria are present. Side effects, however, can be severe. The drug reduces iron levels in the body, so anemia is a common problem. People may need to take iron supplements. Other side effects include nausea, vomiting, depression, anxiety, rash, persistent headache, and, rarely, small blood clots in the legs. This drug is recommended only for people with healthy kidneys whose condition is due to specific struvite-causing organisms. People taking this medicine should avoid alcohol. Pregnant women should not take AHA.
Organic Acids: Medical treatments to dissolve stones may be useful in people who do not respond to other medications, or in combination with surgery. Acidic urine dissolves struvite stones, so the doctor may wash the urinary tract with a solution of organic acids (such as Renacidin). Candidates for such washes must have sterile urine (no bacteria or other organisms in the urine) and healthy kidney function. In surgical patients, the wash is performed 4 or 5 days after the operation. The wash starts with saline (salt solution) for 1 to 2 days. If there are no problems, the organic acid solution follows for another 1 or 2 days, until all stones dissolve. Regular urine tests are necessary to ensure that the bacteria do not return.
The first-line treatment for cystine stones is increasing the alkalization of urine so the stones can dissolve. If alkalization fails, drug treatments may include d-penicillamine, alpha-mercaptopropionylglycine (tiopronin), or captopril. These medications lower cystine concentration.
People with cystine stones must drink much more fluid than people with other stones, at least 4 quarts of water a day.
Surgery is usually needed if:
Today, treatments for stones are much less invasive than in the past. Major surgery is performed in less than 2% of people. Stone removal procedures include the following:
Most procedures are more effective for calcium and uric acid stones and less effective for struvite and cystine stones, although new techniques may be improving their effectiveness on all stones.
Extracorporeal shock wave lithotripsy (SWL) is a technique that uses sound waves (ultrasound) to break up simple stones in the kidney or upper urinary tract. (Extracorporeal means "outside the body," and lithotripsy means "stone-breaking.") SWL is not used for cystine stones. The procedure generally does not work for stones larger than 3 centimeters in diameter (which is slightly over an inch). SWL can often be done on an outpatient basis with limited anesthesia such as IV sedation and topical agents.
There are several variations of SWL. The following is a typical procedure:
The shattered stone fragments may cause discomfort as they pass through the urinary tract. If so, the doctor may insert a small tube called a stent through the bladder into the ureter to help the fragments pass. This practice, however, does not usually speed up passage of the stones and is not used routinely.
Extracorporeal SWL is a procedure used to shatter simple stones in the kidney or upper urinary tract. Ultrasonic waves are passed through the body until they strike the dense stones. Pulses of sonic waves pulverize the stones, which then pass more easily through the ureter and out of the body in the urine.
SWL has a 50 to 90% success rate, depending on the location of the stone and the surgeon's technique and experience. SWL is not as effective as percutaneous nephrolithotomy for stones in the lower kidneys, but it sometimes reduces the length of treatment and the hospital stay. Recovery time is short. Most people can resume their normal activities in a few days.
SWL is considered generally safe, and has few complications. If they do occur, complications may include:
SWL appears to be safe for children. Experts recommend using the least amount of shocks and impact possible in young people. If more than one treatment is needed, the person should wait at least 15 days before having the next treatment.
Ureteroscopy may be used for stones in the middle and lower ureter. Because it uses smaller instruments, this procedure can be done successfully in children.
During ureteroscopic stone removal:
Ureteroscopy achieves a higher stone removal rate than SWL, but it also has a higher risk of complications. In some cases, large stones are not broken up into small enough pieces. This can result in a blockage of the urinary tract and possible kidney damage.
Imaging tests, such as ultrasound or spiral CT, are useful within 3 months to check for residual stones, and a second procedure may be required. The risk of complications is highest when the procedure is performed by less experienced surgeons, or if stones are found in the kidney. The risk for perforation of the ureter increases the longer the procedure takes.
Percutaneous nephrolithotomy (PCNL) may also be used to treat kidney stones. It is often considered when SWL is not available or when the stone is very large, in a difficult to reach location, or is a cystine stone. PCNL is preferred over SWL for stones that have remained in the ureter for more than 4 weeks. PCNL is recommended for stones greater than 20 mm and perhaps for moderate size stones as well (10 to 20 mm).
PCNL is more effective than SWL for people who are severely obese, and it appears to be safe for the very elderly and the very young. Success rates are very high for kidney stones and for ureteral stones; however, success may vary based on the technique used and the specific person. For example, success rates are slightly lower in children, although the procedure can be done safely in young people. Long-term effects are unknown.
A typical procedure is as follows:
Devices Used to Destroy Stone: For large stones, some type of energy-delivering device may be needed to break the stone into small pieces. These are referred to as intracorporeal lithotripsy devices (meaning stone breakers within the body), and may include:
Complications: Advances in technology have reduced the number and severity of complications related to PCNL in recent years. Bleeding during surgery is the most common complication. Post-operative bleeding occurs in about 1% of PCNLs. Tears and injury to nearby organs or structures may also occur. Scarring of the tissue is one possible complication, but studies indicate that this scarring does not impair kidney function. Up to a third of people experience fever after PCNL.
Because the procedure uses large volumes of fluid, fluid overload is a potential problem, particularly in children or people with heart disease.
Infection may occur in some patients. Other serious complications may include a collapsed lung and injuries to areas outside the kidney (but within the operative area), such as the abdomen or chest. But these occurrences are extremely rare.
Open surgery is the least common method for removing stones. It is only performed in a very small percentage of people today. Called nephrolithotomy, it involves making incisions through the person's flank and into the kidney. The surgeon will cool the kidneys using ice. X-rays taken during the procedure help locate the stone. The surgeon will isolate the arteries supplying the kidneys to ensure they are not harmed during the surgery. The surgeon will then locate and remove the stone. The surgeon will also correct any blockage in the affected area.
This surgery is very invasive and therefore is only used for:
Some centers report success with SWL in people who would normally be nephrolithotomy candidates. Therefore, even these people should discuss other options with their surgeon and seek advice from experienced centers.
The procedure is not appropriate for people with:
Between 70 and 90% of crystals remain tiny enough to travel through the urinary tract and leave the body in the urine without being noticed. However, when they do cause symptoms, kidney stones have been described as one of the most painful disorders to afflict humans. The pain they cause is sometimes called renal colic. (Renal means "kidney.")
Obstruction and Infection: Although kidney stones often lead to obstruction (blockage) of the urinary tract, the blockage is usually temporary and causes no lasting damage. In some cases, however, particularly if the obstruction progresses with no symptoms, infection may occur, which can be serious and requires immediate attention.
Chronic Kidney Disease: People with kidney stones face a higher risk for chronic kidney disease, particularly if they also have diabetes, high blood pressure, or frequent urinary tract infections. Having chronic kidney disease, in turn, can increase the risk for a heart attack. Researchers have found that in general, kidney stones increase the risk for a heart attack by more than a third (as well as the risk for certain other disorders), independent of their effect on chronic kidney disease.
Kidney Failure: It is very rare for kidney stones to cause kidney failure. However, some people have risk factors that make them more vulnerable to this serious complication, such as:
Without treatment, calcium stones recur in 40% of people within 5 years of the first attack, and in 75% of people within 20 years. The individual risk for recurrence, however, varies depending on the stone and the underlying condition. For example, a 15-year-old with inherited cystine stones has a very high risk for recurrence, while a middle-aged man with a first calcium oxalate stone has a good chance of never passing another stone.
Anyone who has had kidney stones should try to prevent a recurrence. Some general prevention tips include:
Dietary Considerations: People with kidney stones appear to be more sensitive to certain foods than people who do not form kidney stones. Therefore, vulnerable people should make specific changes in their diet.
Because different kidney stone types may require specific dietary changes, patients should work with their doctors to develop an individualized plan. Tailored nutritional considerations are very important in preventing recurrences, and people should comply with the proper diet. Drinking plenty of fluids is important for preventing a recurrence of any kidney stone.
Indications for Drug Treatments: If dietary treatments fail, drug therapy may be helpful. A number of drugs are available to prevent recurrences of calcium oxalate and other stones. Medications that inhibit the formation of stones include allopurinol, thiazide, potassium citrate, and potassium-magnesium citrate. In addition, drug treatments can sometimes help prevent other complications related to stones, such as osteoporosis.
Correcting Underlying Conditions Known to Cause Kidney Stones: It is also important to treat and correct, if possible, any underlying disorder that may be causing stones to form. Such disorders include distal renal tubular acidosis, hyperthyroidism, sarcoidosis, and certain cancers. To prevent calcium stones that form in hyperparathyroid patients, a surgeon may remove the affected parathyroid gland (located in the neck).
Fluids (Water, Juice, and Other Beverages)
Of all the preventive recommendations, drinking enough fluids is the most important guideline for people with any type of kidney stones.
In all cases, people need more fluid after exertion and during times of stress. If they drink enough, the urine should be pale and almost watery, not dark and yellow.
Water: Water hardness (meaning how much calcium is in the water) generally plays only a small role in stone formation. By far, the amount of fluid intake is most important in preventing stones.
Juices: Other beverages have various effects, depending on the type of stone:
Other Beverages and Their Effects on Stone Formation.
A low-sodium, low-to-moderate protein diet containing normal levels of calcium can help reduce the recurrence of stones compared to a low-calcium only diet.
Salt Restriction: Because salt intake increases the amount of calcium in urine, patients with calcium stones should limit their sodium intake to 1,500 mg or less a day. Sodium may also increase levels of urate, the crystalline substance that can trigger the formation of recurrent calcium oxalate stones.
Protein Restriction: Protein increases uric acid, calcium, and oxalate levels in the urine, and reduces citrate levels. Diets high in protein, particularly meat protein, have been consistently connected with kidney stones. (Meat protein has a higher sulfur content and produces more acid than vegetable protein.)
It is unknown whether restricting meat protein alone without restricting sodium has any protective value. Most studies to date have found no difference in stone development between people with low and normal protein diets.
Although the precise role of dietary protein in kidney stones needs further clarification, it is reasonable for everyone to consume meat protein in moderation. People with struvite stones who need to reduce phosphates in their diets should also cut down on protein.
DASH Diet: The same diet that is recommended to control blood pressure might also reduce the risk of kidney stones. The DASH diet, which is high in fruits and vegetables and low in animal protein, appears to reduce the incidence of kidney stones by as much as 40 to 50%.
Calcium from Foods: Dietary calcium recommendations for kidney stone prevention need to be determined on an individual basis. A doctor will suggest calcium guidelines based on a person's age, gender, body size, and type of stone. General recommendations for daily dietary calcium intake are:
Most studies indicate that people who eat the recommended amount of dietary calcium (found in milk, yogurt, and cheese) have a lower chance of stone recurrence than those who eat a low-calcium diet. Therefore, a diet containing a normal amount of calcium, but reduced amounts of animal protein and salt may protect against stones better than a low-calcium regimen.
Calcium Restriction in Certain Cases: Some people, such as those whose stones are caused by genetic defects in which the intestine absorbs too much calcium, may need to limit calcium intake. More studies are needed to define this group precisely.
Fiber may be beneficial for people with kidney stones. In addition, some fiber-rich foods may contain compounds that help protect against kidney stones. A wide variety of high-fiber plant foods contain a compound called phytate (also called inositol hexaphosphate, InsP6, or IP6), which appears to help prevent the crystallization of calcium salts, both oxalate and phosphate. Phytate is found in legumes and wheat and rice bran. Soybeans are also rich in phytate, but they are also very high in oxalates, so the overall effects of soy on kidney stones are not clear.
A high intake of purines can increase the amount of uric acid in the urine. Those at risk for uric acid stones should reduce their intake of foods and beverages that contain purines.
Some diet and lifestyle changes that may help prevent uric acid stones:
People who have hyperoxaluria will be advised to limit the amount of oxalate in their diet.
Certain fats may play a beneficial or harmful role in specific cases of kidney stones.
Restricted Fats in People with Stones Associated with Bowel Disease: People who have stones associated with short-bowel syndrome should eat foods with lower amounts of fats and oxalates. If people with short-bowel syndrome eat too much fat, calcium may bind to unabsorbed fat instead of to oxalates, increasing oxalate levels and raising the risk of stone formation.
Fish Oil: Omega-3 fatty acids, found in oily fish like mackerel, salmon, and albacore tuna, have many health benefits, but evidence on its impact on kidney stones is limited. More research is necessary to define the benefits, if any.
Vitamin B6: Vitamin B6, or pyridoxine, is used to treat people with primary hyperoxaluria, a severe inherited disorder. People should not try to treat themselves with vitamin B6. Very high doses (500 to 2,000 mg daily over long periods of time) can cause nerve damage. Food sources of vitamin B6 include meats, oily fish, poultry, whole grains, dried fortified cereals, soybeans, avocados, baked potatoes with skins, watermelon, plantains, bananas, peanuts, and brewer's yeast.
Vitamin C: Ascorbic acid (vitamin C) may change in the body to tiny crystals, called oxalates. These crystals do not dissolve. People with hyperoxaluria (too much oxalate in the urine) should avoid vitamin C supplements. Even for men with normal oxalate levels, higher consumption of vitamin C (more than 1,000 mg a day) may increase kidney stone risk.
Healthy weight loss can help improve kidney stone management. Extreme diets with rapid weight loss and selective food intake however can have the opposite effect. People should work with their physician on the most appropriate diet for their type of kidney stone(s).
Because of an association between stress and kidney stones, relaxation and stress management techniques may also be beneficial.
Diet and Lifestyle
Plenty of fluids. (Choose water, lemon juice. Avoid grapefruit, apple, and cranberry juice.)
Limit the amount of protein and salt in the diet.
Limit the amount of fats in the diet, particularly in people who have short bowel syndrome.
Balance normal calcium intake with potassium- and phosphate-rich foods.
Limit the amount of calcium in the diet (only in people who have genetic abnormalities that cause high intestinal absorption of calcium).
Limit the amount of foods high in oxalates (only in people with rare intestinal conditions that cause hyperoxaluria).
Diuretics (water pills), citrate salts, phosphates, and cholestyramine
Lithotripsy, uteroscopy, percutaneous nephrolithotomy, and open surgery
Plenty of fluids. (Choose water, blackcurrant juice. Avoid cranberry juice.)
Increase calcium intake (be sure it is well-balanced with potassium and phosphates and taken with food).
Reduce protein and other foods with high purine content.
Limit alcohol intake.
Diabetes patients should add coffee and tea to their diets.
Potassium citrate, sodium bicarbonate, and allopurinol
Lithotripsy, uteroscopy, percutaneous nephrolithotomy, and open surgery
Plenty of fluids (water, cranberry juice)
Increase caffeine intake (diabetics)
Antibiotics to eliminate any infection. Acetohydroxamic acid (AHA) may be helpful in combination with antibiotics. In some cases, organic acids are given through the urinary tract.
May respond poorly to most lithotripsy procedures and require open surgery. Newer procedures may be helpful.
Very high fluid intake (4 quarts a day)
Limit the amount of protein in the diet.
Decrease dairy, legumes, chocolate, and nuts.
Alkalizing agents (such as bicarbonate). Sometimes d-penicillamine, tiopronin, or captopril is useful for lowering cystine levels.
May respond poorly to most lithotripsy procedures and require open surgery. Newer procedures may be helpful.
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Review Date: 8/30/2013
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team. Editorial update: 05-11-2015.
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