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Stones in the Urinary Tract

(Kidney Stones; Urinary Calculi; Urolithiasis)


Glenn M. Preminger

, MD, Duke Comprehensive Kidney Stone Center

Reviewed/Revised Apr 2023
Topic Resources

Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine.

Urinary tract stones form in a kidney and may pass into a ureter or the bladder. Depending on where a stone is located, it may be called a kidney stone, ureteral stone, or bladder stone. The process of stone formation is called urolithiasis, renal lithiasis, or nephrolithiasis.

The Urinary Tract

The Urinary Tract

Every year, about 1 of 1,000 adults in the United States are hospitalized because of stones in the urinary tract. Stones are more common among middle-aged and older adults. Stones vary in size from too small to be seen with the naked eye to 1 inch (2.5 centimeters) or more in diameter. A large, so-called staghorn (because of its many projections that resemble a deer's antlers) stone may fill almost the entire renal pelvis (the central collecting chamber of the kidney) and the tubes that drain into it (calyces).

Inside the Kidney

Inside the Kidney

A urinary tract infection Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria... read more may result when bacteria become trapped in urine that pools above a blockage. When stones block the urinary tract for a long time, urine backs up in the tubes inside the kidney, causing excessive pressure that can cause the kidney to swell (hydronephrosis Hydronephrosis: A Distended Kidney Hydronephrosis: A Distended Kidney ) and eventually damage it.

Types of stones

Stones are made of minerals in the urine that form crystals. Sometimes the crystals grow into stones. About 85% of the stones are composed of calcium, and the remainder are composed of various substances, including uric acid, cystine, or struvite. Struvite stones—a mixture of magnesium, ammonium, and phosphate—are also called infection stones, because they form only in infected urine.

Causes of Urinary Tract Stones

Stones may form because the urine becomes too saturated with salts that can form stones or because the urine lacks the normal inhibitors of stone formation. Citrate is such an inhibitor because it normally binds with calcium that is often involved in forming stones.

Rarely, medications (including indinavir) and substances in the diet (such as melamine) cause stones.

Symptoms of Urinary Tract Stones

Stones, especially tiny ones, may not cause any symptoms. Stones in the bladder may cause pain in the lower abdomen. Stones that obstruct the ureter or renal pelvis or any of the kidney’s drainage tubes may cause back pain or renal colic. Renal colic is characterized by an excruciating intermittent pain, usually in the area between the ribs and hip on one side, that spreads across the abdomen and often extends to the genital area. The pain tends to come in waves, gradually increasing to a peak intensity, then fading, over about 20 to 60 minutes. The pain may radiate down the abdomen toward the groin or testis or vulva.

Other symptoms include nausea and vomiting, restlessness, sweating, and blood or a stone or a piece of a stone in the urine. A person may have an urge to urinate frequently, particularly as a stone passes down the ureter. Chills, fever, burning or pain during urination, cloudy, foul-smelling urine, and abdominal swelling sometimes occur.

Diagnosis of Urinary Tract Stones

  • Symptoms

  • Computed tomography (CT)

Doctors usually suspect stones in people with renal colic. Sometimes doctors suspect stones in people with tenderness over the back and groin or pain in the genital area without an obvious cause. Finding blood in the urine supports the diagnosis, but not all stones cause blood in the urine. Occasionally, the symptoms and physical examination findings are so distinctive that no additional tests are needed, particularly in people who have had urinary tract stones before. However, most people are in so much pain and have symptoms and findings that make other causes for the pain seem likely enough that testing is necessary to exclude these other causes. Doctors need to differentiate stones from other possible causes of severe abdominal pain, including

Helical (also called spiral) CT Computed tomography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating... read more done without the use of radiopaque contrast material Radiographic Contrast Agents Radiographic contrast agents are substances used to distinguish between internal structures in medical imaging, such as various types of x-rays and magnetic resonance imaging (MRI). During imaging... read more is usually the best diagnostic procedure. CT can locate a stone and also indicate the degree to which the stone is blocking the urinary tract. CT can also detect many other disorders that can cause pain similar to the pain caused by stones. The main disadvantage of CT is that it exposes people to radiation. Still, this risk seems prudent when possible causes include another serious disorder that would be diagnosed by CT, such as an aortic aneurysm Aortic Branch Aneurysms Aortic branch aneurysms are bulges (dilations) in the wall of the major arteries that come directly off of the aorta. (See also Overview of Aortic Aneurysms and Aortic Dissection.) The aorta... read more or appendicitis Appendicitis Appendicitis is inflammation and infection of the appendix. Often a blockage inside the appendix causes the appendix to become inflamed and infected. Abdominal pain, nausea, and fever are common... read more . Newer CT devices and methods that limit exposure to radiation are now commonly used.

Ultrasonography Ultrasonography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating... read more is an alternative to CT and does not expose people to radiation. However, ultrasonography, compared with CT, more often misses small stones (especially when located in the ureter), the exact location of urinary tract blockage, and other serious disorders that could be causing the symptoms.

Did You Know...

  • People who have recurrent kidney stones should consider limiting the number of CT scans they get to prevent excessive radiation exposure.

X-rays Plain x-rays There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating... read more of the abdomen expose people to much less radiation than does CT, but x-rays are much less accurate in diagnosing stones and can show only calcium stones. When doctors suspect the person has a calcium stone, x-rays are an alternative to confirm the presence of a stone or to see how far a stone has traveled down the ureter.

Excretory urography Intravenous urography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating... read more (previously called intravenous urography or intravenous pyelography) is a series of x-rays taken after intravenous injection of a radiopaque contrast agent. This test can detect stones and accurately determine the degree to which they are blocking the urinary tract, but it is time-consuming and involves the risks of exposure to the contrast agent (for example, an allergic reaction or worsening of kidney failure Overview of Kidney Failure Kidney failure is the inability of the kidneys to adequately filter metabolic waste products from the blood. Kidney failure has many possible causes. Some lead to a rapid decline in kidney function... read more ). Doctors rarely use excretory urography to diagnose stones if CT or ultrasonography is available.

Determining stone type

For people with diagnosed stones, doctors often do tests to determine the type of stones. People should attempt to retrieve stones that are passed. They can retrieve stones by straining all urine through a paper or mesh filter. Stones found can be analyzed. Depending on the type of stone, urine and blood tests may be necessary to measure levels of calcium, uric acid, hormones, and other substances that may increase the risk of stone formation.

Treatment of Urinary Tract Stones

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) or opioids as needed to relieve pain

  • Sometimes stone removal

Small stones that are not causing symptoms, blockage of the urinary tract Urinary Tract Obstruction Urinary tract obstruction is a blockage that inhibits the flow of urine through its normal path (the urinary tract), including the kidneys, ureters, bladder, and urethra. Blockage can be complete... read more , or an infection usually do not need to be treated and often pass on their own. Larger stones (over three sixteenths of an inch [5 mm]) and those that are closer to the kidney are less likely to pass on their own.

Pain relief

The pain of renal colic may be relieved with NSAIDs. If the pain is severe, opioids are sometimes needed.

Stone-passing strategies

Drinking plenty of fluids or receiving large amounts of fluids intravenously has been recommended to help stones pass, but it is not clear that this approach is helpful. Alpha-adrenergic blockers (such as tamsulosin) may help the stone pass. Once a stone has passed, no other immediate treatment is needed.

Stone-bypass procedures

Sometimes when a blockage is severe, doctors insert a temporary tube (stent) in the ureter to bypass the obstructing stone. Doctors insert a telescopic viewing instrument (cystoscope, a kind of endoscope) into the bladder and pass the stent through the cystoscope and into the opening of the ureter. The stent is pushed up past the obstructing stone. The stent is left in place until the stone can be removed (for example, by surgery).

Alternatively, doctors may drain the blockage by inserting a drainage tube through the back into the kidney (nephrostomy tube).

Stone removal

Often, shock wave lithotripsy can be used to break up a stone in the renal pelvis or uppermost part of the ureter that is ½ inch (1 centimeter) or less in diameter. In this procedure, shock waves directed at the body by a sound wave generator break up the stone. The pieces of stone are then passed in the urine.

Removing a Stone With Sound Waves

Kidney stones can sometimes be broken up by sound waves produced by a lithotriptor in a procedure called extracorporeal shock wave lithotripsy (SWL).

After an ultrasound device or fluoroscope is used to locate the stone, the lithotriptor is placed against the back, and the sound waves are focused on the stone, shattering it. Then the person drinks fluids to flush the stone fragments out of the kidney, to be eliminated in the urine.

Sometimes blood appears in the urine or the abdomen is bruised after the procedure, but serious problems are rare.

Removing a Stone With Sound Waves

A ureteroscope (a small viewing telescope, a kind of endoscope) can be inserted into the urethra, through the bladder, and up the ureter to remove small stones in the lower part of the ureter that require removal. In some instances, the ureteroscope can also be used with a device to break up stones into smaller pieces that can be removed with the ureteroscope or passed in the urine (a procedure called intracorporeal lithotripsy). Most commonly, holmium laser lithotripsy is used. In this procedure, a laser is used to break up the stone.

Percutaneous nephrolithotomy may be used to remove some larger kidney stones. In percutaneous nephrolithotomy, doctors make a small incision in the person's back and then insert a telescopic viewing tube (called a nephroscope, a kind of endoscope) into the kidney. Doctors insert a probe through the nephroscope to break the stone into smaller pieces and then remove the pieces (nephrolithotripsy).

Making the urine more alkaline (for example, with potassium citrate taken for 4 to 6 months by mouth) may sometimes gradually dissolve uric acid stones. Other types of stones cannot be dissolved this way.

Surgical removal is sometimes needed for larger stones that are causing an obstruction.

Endoscopic surgery is usually used to remove struvite stones. Antibiotics are not helpful in treating urinary tract infections Urinary Tract Infections (UTIs) until the infection stones are completely removed.

Ureteral stenting is the placement of a soft hollow tube to help urine drain from the kidney to the bladder. A ureteral stent may be necessary for a week or two after a procedure done to remove a stone. Irritation from the stone or from the removal procedure could cause some inflammation of the ureter. The stent helps the inflammation resolve.

Prevention of Urinary Tract Stones

In a person who has passed a calcium stone for the first time, the likelihood of forming another stone is about 15% within 1 year, 40% within 5 years, and 80% within 10 years. Measures to prevent the formation of new stones vary, depending on the composition of the existing stones.

Drinking large amounts of fluids—8 to 10 ten-ounce (300-milliliter) glasses a day—is recommended for prevention of all stones. People should drink enough fluid to produce more than about 2 quarts of urine per day. Other preventive measures depend somewhat on the type of stone.

Calcium stones

People with calcium stones may have a condition called hypercalciuria, in which excess calcium is excreted in the urine. For these people, measures that decrease the amount of calcium in the urine can help prevent formation of new stones. One such measure is a diet that is low in sodium and high in potassium. Calcium Overview of Calcium's Role in the Body Calcium is one of the body's electrolytes, which are minerals that carry an electric charge when dissolved in body fluids such as blood, but most of the body's calcium is uncharged. (See also... read more intake should be about normal—1,000 to 1,500 milligrams daily (about 2 to 3 servings of dairy per day). The risk of a new stone forming is actually higher if the diet contains too little calcium, so people should not try to eliminate calcium from their diet. However, people may need to avoid sources of excess calcium such as antacids that contain calcium.

Thiazide diuretics, such as chlorthalidone or indapamide, also reduce the concentration of calcium in the urine in such people. Potassium citrate may be given to increase a low urine level of citrate, a substance that inhibits calcium stone formation. Restricting dietary animal protein may help reduce urinary calcium and the risk of stone formation in many people with calcium stones.

Did You Know...

  • People who have calcium stones are more likely to develop other stones if their diet has too little or too much calcium.

A high level of oxalate in the urine, which contributes to calcium stone formation, may result from excess consumption of foods high in oxalate, such as rhubarb, spinach, cocoa, nuts, pepper, and tea, or from certain intestinal disorders (including some kinds of weight loss surgery). Calcium citrate, cholestyramine, and a diet that is low in fat and in oxalate-containing food may help to reduce urinary oxalate levels in some people. Pyridoxine (vitamin B6) decreases the amount of oxalate the body makes.

Uric acid stones

Uric acid stones are almost always caused by excessive acid levels in the urine. Potassium citrate should be given to all people who have uric acid stones to make the urine alkaline and neutralize the high acid levels that cause uric acid stones. Occasionally, a low animal protein diet or allopurinol may be used to reduce uric acid levels in the urine. Maintaining a large fluid intake is also very important.

Cystine stones

For stones made of cystine, urinary cystine levels must be kept low by maintaining a large fluid intake and sometimes taking alpha-mercaptopropionylglycine (tiopronin) or penicillamine.

Struvite stones

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