Kidney Stones in Adults

On this page:

• Introduction to the Urinary Tract
• What is a kidney stone?
• Who gets kidney stones?
• What causes kidney stones?
• What are the symptoms?
• How are kidney stones diagnosed?
• How are kidney stones treated?
• Kidney Stone Prevention
• Surgical Treatment
• For More Information
• Additional Reading

Kidney stones, one of the most painful of the urologic disorders, are not a product of modern life. Scientists have found evidence of kidney stones in a 7,000-year-old Egyptian mummy. Unfortunately, kidney stones are one of the most common disorders of the urinary tract. An estimated 10 percent of people in the United States will have a kidney stone at some point in their lives. Men tend to be affected more frequently than women.

Most kidney stones pass out of the body without any intervention by a physician. Stones that cause lasting symptoms or other complications may be treated by various techniques, most of which do not involve major surgery. Research advances have led to a better understanding of the many factors that promote stone formation and led to better strategies for prevention of kidney stones.

Introduction to the Urinary Tract

The urinary tract, or system, consists of the kidneys, ureters, bladder, and urethra. The kidneys are two bean-shaped organs located below the ribs toward the middle of the back. The kidneys remove extra water and wastes from the blood, converting it to urine. They also keep a stable balance of salts and other substances in the blood. The kidneys produce hormones that help build strong bones and help form red blood cells.

Narrow muscular tubes called ureters push the urine from the kidneys to the bladder, a oblong chamber deep in the lower abdomen behind the pubic bone. Like a balloon, the bladder's elastic walls stretch and expand to store urine. They flatten together when urine is emptied through the urethra to outside the body.

What is a kidney stone?

Urolithiasis is the medical term used to describe stones occurring in the urinary tract. Other frequently used terms are urinary tract stones and nephrolithiasis. Doctors also use terms that describe the location of the stone in the urinary tract, such as kidney stone or ureteral stone. All of these stones start in the kidney, so to keep things simple the term "kidney stones" is used throughout this fact sheet.

Our urine contains many chemical substances and salts and minerals. Some of these minerals will form microscopic crystals in the urine. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without being noticed. A kidney stone is a hard "rock" that forms when the crystals build up in the drainage portion of the kidney. Minerals in the urine can crystallize into stones if the urine is too concentrated or if there is too much of certain minerals in the urine. The urine also contains chemicals that prevent crystals from forming. Some patients have too little of these stone inhibitors in the urine, and are at increased risk of stones.

5 Common Types of Kidney Stones

Calcium oxalate

Calcium phosphate (frequently mixed with calcium oxalate)

Uric Acid

Struvite (infection stones)

Cystine

There are several different types of kidney stones, and each has different causes.

Approximately 85% of kidney stones are calcium stones, in combination with either oxalate or phosphate, or both. Calcium, oxalate, and phosphate are part of a person's normal diet and make up important parts of the body, such as bones and muscles.

The second most common type of stones (roughly 10%) are uric acid stones. Uric acid is a breakdown product of protein, and we all have uric acid in our urine. Some people have too much uric acid in the blood, and this can cause a painful type of arthritis called gout. About 1/3 of people with gout will have kidney stones. Other people have normal uric acid levels in the blood but pass too much uric acid into the urine, and are at higher risk of uric acid stones.

The third most common type of stone are caused by urinary infection. These stones are called struvite stones, or magnesium-ammonium-phosphate stones. Struvite stones happen if a patient has a urinary infection with a type of bacteria called a urea-splitting bacteria. It is simply random, bad luck to have an infection with this type of bacteria. The most common urea-splitting bacteria is called Proteus mirabilis. Struvite stones contain bacteria trapped in them and can be very large, and infections and stones can re-occur if the stones are not completely removed.

Rare types of kidney stones include cystine stones and Indinavir stones. Cystine stones are caused by a genetic abnormality that is inherited and causes patients to pass very large amounts of an amino acid called cysteine in the urine. These patients may have many kidney stones throughout their lifetime. Indinavir stones occur in certain patients with AIDS who are taking the drug Indinavir.

Gallstones and kidney stones are not related. They form in different areas of the body. If you have a gallstone, you are not necessarily more likely to develop kidney stones.

Who gets kidney stones?

For unknown reasons, the number of people in the United States with kidney stones has been increasing over the past 20 years. White Americans are more prone to develop kidney stones than African Americans. Stones occur slightly more frequently in men than women.The age when kidney stones first cause problems is usually between 20 and 40, although children will rarely have stones. If a patient has a single stone there is a two-thirds chance that he or she will develop more stones in their lifetime.

What causes kidney stones?

There are many causes of kidney stones, and the cause differs for each type of stone. The risk factor that is common for all types of stones is dehydration. This causes the urine to more concentrated, which makes crystallization of minerals into stones much more likely to occur.

Diet may play a role in certain patients. The most common cause of calcium stones is over absorption of calcium from the food. This condition, called absorptive hypercalciuria, is most likely genetic and people without intestinal over absorption of calcium will usually not get stones no matter how much calcium they eat. Once the body has absorbed too much calcium the only way it can get rid of the extra calcium is in the urine. There is no way to know if you have this condition because it causes no other symptoms other that the tendency for stones. Dietary restriction may help patients with milder forms of absorptive hypercalciuria, but many patients need to take medication to prevent stones. Severe dietary calcium restriction is not recommended for most patients with calcium stones, and can sometimes make a stone condition worse, and should not be done without instructions from your doctor.

Dietary intake of oxalate can also play a role in the formation of calcium oxalate stones. Approximately 20% of the oxalate in the urine comes from our diet, and 80% is made by our own body. Patients who eat large amounts of food high in oxalate can have an increased risk of stones. A diet high in meat (animal protein) can cause higher levels of uric acid in the urine and increase the risk of uric acid stones. Patients who eat a high protein diet, such as the Atkins Diet, may also increase the chance of calcium stone formation.

Other risk factors for calcium stones include prolonged bedrest and use of medications called steroids. A condition called hyperparathyroidism, which causes over-production of a hormone which raises calcium levels in the blood, has a very high chance of stone disease. An inherited kidney disease called renal tubular acidosis also has a very high chance of calcium stone disease. Patients who overuse laxatives, eat excessive amounts of vitamin D, or have chronic diarrhea or severe intestinal problems such as Crohn's disease may also increase the risk of kidney stones. Obstruction of the urinary system causes urine to pool in the kidney and increases the risk of stones. Some patients with elevated uric acid in the urine may develop tiny uric acid crystals which can become covered with calcium oxalate and form calcium stones.

Urinary infection with bacteria called urea-splitting bacteria can cause stones called struvite stones (also known as infection stones). There are a number of urea-splitting bacteria, the most common is called Proteus mirabilis. Infections with urea-splitting bacteria are no different than other urinary tract infections, and it is bad luck to have this type of infection. Infection stones can grow very large and fill the entire kidney. These large stones are called "staghorn" stones because they resemble the branched horns of a male deer.

Gout is a medical condition caused by elevated uric acid levels in the blood. These patients have a painful type of arthritis, and 30% will have uric acid stones. Uric acid stones also form in patients with abnormally acidic urine, particularly if they are dehydrated. Many of these patients have low levels of a natural inhibitor of stones called citrate, and may benefit from citrate supplements. Cystinuria and hyperoxaluria are two rare, inherited metabolic disorders that often cause kidney stones. Patients with cystinuria can not break down certain amino acids and excrete large amounts in the urine. The amino acid cysteine forms crystals which dissolve very poorly in the urine and increase in size to form multiple stones. Patients with hyperoxaluria produces too much oxalate which is passed in the urine. When there is more oxalate than can be dissolved in the urine, oxalate can crystallize with calcium to form calcium oxalate stones.

What are the symptoms?

The first symptom of a kidney stone is usually pain, but sometimes it can be blood in the urine or fever. The pain often begins suddenly when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain in the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur. If the stone is in the lower ureter there may be pain in the lower abdomen, groin, or testicle. As the stone moves down the ureter closer to the bladder, patients may feel the need to urinate more often or feel a burning sensation during urination.

Most smaller stones do not cause pain while they are in the kidney because they are not blocking the kidney. When the stone moves into the ureter the walls of the ureter squeeze and push the stone down the ureter into the bladder. Once the stone passes into the bladder it passes out painlessly in the urine. If the stone is too large to pass easily it can block the ureter which causes the kidney to swell, and causes pain and nausea.

If fever and chills accompany any of these symptoms, an infection may be present. In this case, you should contact a doctor immediately.

How are kidney stones diagnosed?

When a patient has pain that is suspicious for kidney stones x-rays are performed to determine the number, size and location of the stones. Most calcium stones can be seen on a plain x-ray, but they may be difficult to see if they are overlying the bones of the pelvis or are small. Uric acid stones are invisible to plain x-rays and cannot be seen on a simple abdominal x-ray. The best test to find kidney stones is a CT scan, because this type of x-ray can find even tiny stones and shows the number and location of stones in the kidney or ureter. CT scans can also detect uric acid stones that cannot be seen on plain x-rays. An ultrasound can detect stones in the kidney and can show if a kidney is blocked, but it cannot easily find stones in the ureter. The treatment options for stones depend on the stone type, size, number, location, and the patient's symptoms.

How are kidney stones treated?

Most kidney stones that are smaller than 6 mm (1/4 inch) in diameter can pass through the urinary system with plenty of water (2 to 3 quarts a day) to help move the stone along. Often, you can stay home during this process, drinking fluids and taking pain medication as needed. The doctor usually asks you to save the passed stone(s) for testing. (You can catch it in a cup or tea strainer used only for this purpose.) Stones that are too large to pass, or stones that are causing intolerable pain or vomiting, or that are associated with a urinary tract infection will usually need some sort of prompt treatment. Only uric acid stones can be dissolved with medication. The dissolution process is slow, but if a patient is not having a lot of pain and the kidney is not blocked, then it is safe to try medication. Unfortunately, calcium stones cannot be dissolved once they have formed.

Surgery may be needed to remove a kidney stone if it:

• does not pass after a reasonable period of time and causes constant pain
• is too large to pass on its own or is caught in a difficult place
• blocks the flow of urine
• causes ongoing urinary tract infection
• damages kidney tissue or causes constant bleeding
• has grown larger (as seen on followup x ray studies)

Ninety-nine percent of kidney stones can be removed by surgery with telescopes or by shockwave treatments, and traditional surgery involving prolonged recovery is exceedingly rare in the modern era.

Extracorporeal Shockwave Lithotripsy

Extracorporeal shockwave lithotripsy (ESWL) is the most frequently used procedure for the treatment of kidney stones. In ESWL, shock waves that are created outside the body travel through the skin and body tissues until they hit the denser stones. The stones break down into sand-like particles and are easily passed through the urinary tract in the urine.

There are several types of ESWL devices. In older devices the patient reclines in a water bath while the shock waves are transmitted. Newer devices have a table on which the patient lies. Most devices use x-rays to pinpoint the stone during treatment. For most types of ESWL procedures, some type of anesthesia is needed. In most cases, ESWL may be done on an outpatient basis. Recovery time is short, and most people can resume normal activities in a few days.

Complications may occur with ESWL. Most patients have blood in their urine for a few days after treatment. Bruising and minor discomfort in the back or abdomen from the shock waves are also common. To reduce the risk of complications, doctors usually tell patients to avoid taking aspirin and other drugs that affect blood clotting for 7-10 before treatment.

Another complication may occur if the shattered stone particles cause discomfort as they pass through the urinary tract. In some cases, the doctor will insert a small tube called a stent through the bladder into the ureter to help the fragments pass. Sometimes the stone is not completely shattered with one treatment, and additional treatments may be needed. ESWL is not ideal when stones are larger than 2 centimeters because several shock wave treatments will be necessary and the large amount of stone particles will plug the ureter and require other treatments.

Percutaneous Nephrolithotomy

Percutaneous nephrolithotomy is used when the stone is very large (>2 cm) or in a location that does not allow effective use of ESWL. In this procedure, the patient initially goes to the radiology suite where a tube or wires are placed into the kidney under x-ray guidance. The patient is then take to the operating room where the urologist makes a tiny incision in the back and passes a tube over the wire into the kidney. A telescope called a nephroscope is passed through the tube into the kidney and the urologist locates and removes the stone. For large stones, some type of energy probe (ultrasonic or laser) may be needed to break the stone into small pieces before they can be removed. Patients usually stay in the hospital for 1-2 days and may have a small tube called a nephrostomy tube left in the kidney for one week during the healing process. If the stones are not removed entirely in the initial procedure a "second look" procedure may be performed several days later to remove any remaining stones. One advantage of percutaneous nephrolithotomy over ESWL is that the surgeon removes the stone fragments instead of relying on their natural passage from the kidney.

Ureteroscopic Stone Removal

Although some kidney stones in the upper ureters can be treated with ESWL, it is not usually effective for stones that are below the pelvic bones because the shock waves are blocked by the bones. These stones are usually removed by a procedure called ureteroscopy, which has a 95% success rate in removing or breaking up the stone in a single procedure. The urologist passes a small fiber optic telescope called a ureteroscope through the urethra and bladder into the ureter. The urologist passes the telescope under direct vision until he sees the stone and either removes it with a cage-like device or shatters it with a laser. A small tube called a stent may be left in the ureter for a few days to help the lining of the ureter heal. Before fiber optics made ureteroscopy possible, physicians used a similar "blind basket" extraction method, but this outdated technique should not be used because it may damage the ureters.

Kidney Stone Prevention

If you've had more than one kidney stone, you are likely to form another; so prevention is very important. To prevent stones from forming, your doctor must determine their cause. He or she will order laboratory tests, including urine and blood tests. Your doctor will also ask about your medical history, occupation, and eating habits. If a stone has been removed, or if you've passed a stone and saved it, the laboratory should analyze it because its composition helps in planning treatment.

You may be asked to collect your urine for 24 hours after a stone has passed or been removed. The sample is used to measure urine volume and levels of acidity, calcium, sodium, uric acid, oxalate, citrate, phosphorous, and creatinine (a product of muscle metabolism). Your doctor will use this information to determine the cause of the stone. A second 24-hour urine collection may be needed to determine whether the prescribed treatment is working.

Lifestyle Changes

A simple and most important lifestyle change to prevent stones is to drink more liquids--water is best. If you tend to form stones, you should try to drink enough liquids throughout the day to produce at least 2 quarts of urine in every 24-hour period.

People who form calcium stones used to be told to avoid dairy products and other foods with high calcium content. But recent studies have shown that most patients with kidney stones have a lower risk of recurrence if they take in the recommended daily amount of calcium instead of severely restricting their calcium intake. The main source of calcium is dairy products and dark leafy greens. The recommended total daily calcium intake is 1000 mg per day, or 3 servings of dairy products per day. Patients should avoid taking calcium in pill form (Tums or Rolaids or calcium supplements), however, because this may increase the risk of developing stones.

Patients with stones should eat as low-salt, low protein diet as they can to lower the risk of stones. Patients with high urinary oxalate should limit or avoid foods that are high in oxalate, including:

• dark, leafy greens such as chard, spinach, or kale
• beets
• chocolate
• coffee
• cola
• nuts
• rhubarb
• strawberries
• tea
• wheat bran

People should not give up or avoid eating these foods without talking to their doctor first. In most cases, these foods can be eaten in limited amounts.

Medical Therapy

Patients with recurrent stones despite dietary and lifestyle changes may benefit from medical therapy. Potassium citrate supplements (Urocit-K, Mission Pharmacal) have been shown to lower the recurrence rate of calcium stones, and is a safe, well tolerated substance that is made of natural chemicals that are not foreign to our bodies. Some patients with excess calcium in the urine may take a diuretic such as hydrochlorothiazide, which decreases the amount of calcium in the urine. These drugs decrease the amount of calcium released by the kidneys into the urine by favoring calcium retention in bone. They work best when sodium intake is low. Patients with severe hypercalciuria that does not respond to calcium restriction may rarely be given the drug sodium cellulose phosphate, which binds calcium in the intestines and prevents it from being absorbed into the body.

Patients with elevated uric acid levels in the blood should take allopurinol to prevent uric acid stones and gout.

Cystine stones are treated by increasing fluid intake to 4-5 liters per day and by taking medication to raise the pH of the urine to more thn 7.0. If this is unsuccessful in preventing stones, your doctor may prescribe drugs such as Thiola and Cuprimine, which can help to reduce the amount of cystine in the urine.

For struvite stones that have been totally removed, the first line of prevention is to keep the urine free of bacteria that can cause infection. Your urine will be tested regularly to be sure that no bacteria are present. If struvite stones cannot be removed, your doctor may prescribe a drug called acetohydroxamic acid (AHA). AHA is used with long-term antibiotic drugs to prevent the infection that leads to stone growth.

People with hyperparathyroidism sometimes develop calcium stones. Treatment in these cases is usually surgery to remove the parathyroid glands (located in the neck). In most cases, only one of the glands is enlarged. Removing the glands cures the patient's problem with hyperparathyroidism and with kidney stones as well.

Prevention Points to Remember:

• If you have a family history of stones or have had more than one stone, you are likely to develop more stones.
• A good first step to prevent the formation of any type of stone is to drink plenty of liquids-water is best.
• If you are at risk for developing stones, your doctor may perform certain blood and urine tests to determine which factors can best be altered to reduce that risk.
• Some people will need medicines to prevent stones from forming.
• People with chronic urinary tract infections and stones will often need the stone removed if the doctor determines that the infection results from the stone's presence. Patients must receive careful followup to be sure that the infection has cleared.