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Pronunciations allopurinol aneurysm appendicitis computed tomography extracorporeal shock wave lithotripsy hydronephrosis hyperparathyroidism lithiasis lithotripsy opioids penicillamine pyridoxine sarcoidosis ultrasonography ureter urethra urolithiasis

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

Stones in the Urinary Tract

• Tiny stones may cause no symptoms, but larger stones can cause excruciating pain in the area between the ribs and hips.
• Usually, an imaging test and an analysis of urine are done to diagnose stones.
• Sometimes, stone formation can be prevented by changing the diet.
• Stones that do not pass on their own are removed with lithotripsy or an endoscopic technique.

Depending on where a stone forms, it may be called a kidney stone, ureteral stone, or bladder stone. The process of stone formation is called urolithiasis, renal lithiasis, or nephrolithiasis.

Every year, about 1 of 1,000 adults in the United States is hospitalized because of stones in the urinary tract. Stones are more common in middle-aged and older adults and in men. 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 stone may fill almost the entire renal pelvis (small tubes of the kidney and its collecting area) and the tubes that drain into it (calices).

A urinary tract infection 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, producing excessive pressure that can distend the kidney (hydronephrosis) and eventually damage it.

Causes

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 the calcium that is often involved in forming stones. About 80% of the stones are composed of calcium, and the remainder are composed of various substances, including uric acid, cystine, and struvite. Stones are more common in people with certain disorders (for example, hyperparathyroidism and short bowel syndrome) and in people whose diet is very high in protein or vitamin C or who do not consume enough water or calcium. People who have a family history of stone formation are more likely to have calcium stones and to have them more often. Struvite stones—a mixture of magnesium, ammonium, and phosphate—are also called infection stones, because they form only in infected urine.

Symptoms

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 flank (the area between the ribs and hip), that spreads across the abdomen, often to the genital area and inner thigh. 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 testicle or vulva.

Other symptoms include nausea and vomiting, restlessness, sweating, and blood in the urine. A person may have an urge to urinate frequently, particularly as a stone passes down the ureter. Chills, fever, and abdominal distention sometimes occur.

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

Diagnosis

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. 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. Helical (also called spiral) computed tomography (CT) that is done without the use of radiopaque contrast material 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 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 or appendicitis. Ultrasonography 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 location of urinary tract blockage, and other, serious disorders that could be causing the symptoms.

Urinalysis is usually done. It may show blood or pus in the urine whether or not symptoms are present.

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. Stones found can be analyzed. Depending on the type of stone, urine tests and tests of blood chemistries and hormone levels may be necessary.

Prevention

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, although it is not clear whether and how much this helps. Many people with calcium stones have a condition called hypercalciuria, in which excess calcium is excreted in the urine. For them, a diet that is low in sodium and high in potassium may also help. Calcium intake should be about normal, 1000 to 1500 mg daily (see Minerals and Electrolytes: Calcium). Restricting dietary protein from red meat may help reduce the risk of stone formation. Thiazide diuretics, such as chlorthalidoneSome Trade Names
HYGROTON
or indapamideSome Trade Names
LOZOL
, reduce the concentration of calcium in the urine and help prevent the formation of new stones in such people. Potassium citrate may be given to increase a low urine level of citrate, a substance that inhibits calcium stone formation.

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. Calcium citrate, cholestyramineSome Trade Names
QUESTRAN
, and a low-oxalate, low-fat diet may help to reduce urinary oxalate levels in some people. Sometimes pyridoxine decreases the amount of oxalate the body makes.

In rare cases, when calcium stones result from hyperparathyroidism, sarcoidosis, vitamin D toxicity, renal tubular acidosis, or cancer, the underlying disorder must be treated.

For stones that contain uric acid, a diet low in red meat, is recommended, because red meat increases the level of uric acid in the urine. If this is not effective, allopurinolSome Trade Names
LOPURIN
ZYLOPRIM
may be given to reduce the production of uric acid. Potassium citrate should be given to all people who have uric acid stones to make the urine alkaline, because uric acid stones form when urine acidity increases. Maintaining a large fluid intake is also very important.

For stones made of cystine, urinary cystine levels must be kept low by maintaining a large fluid intake and sometimes taking α-mecaptopropionylglycine (tioproninSome Trade Names
THIOLA
) or d-penicillamineSome Trade Names
CUPRIMINE
.

People with recurrent struvite stones may need to take antibiotics continually to prevent urinary tract infections. Acetohydroxamic acid may also be helpful.

Treatment

Small stones that are not causing symptoms, obstruction, or an infection usually do not need to be treated. 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. Drugs that may help the stone pass include alpha-adrenergic blockers (such as tamsulosinSome Trade Names
FLOMAX
) and calcium channel blockers (such as diltiazemSome Trade Names
CARDIZEM
DILACOR
, nifedipineSome Trade Names
ADALAT
PROCARDIA
, and verapamilSome Trade Names
CALAN
ISOPTIN
). Once a stone has passed, no other immediate treatment is needed. The pain of renal colic may be relieved with nonsteroidal anti-inflammatory drugs (NSAIDs) or opioids.

Often, a stone in the renal pelvis or uppermost part of the ureter that is ½ inch (1 centimeter) or less in diameter can be broken up by shock waves directed at the body by a sound wave generator (a procedure called extracorporeal shock wave lithotripsy). The pieces of stone are then passed in the urine. Sometimes, a stone is removed with grasping forceps using an endoscope (viewing tube) through a small incision in the skin, or the stone can be shattered into fragments using a probe from a lithotripsy machine and then the pieces are 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. 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.

Extracorporeal Shock Wave Lithotripsy

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

Uric acid stones may sometimes be dissolved gradually by making the urine more alkaline (for example, with potassium citrate taken for 4 to 6 months by mouth), but other types of stones cannot be dissolved this way. Sometimes, larger stones that are causing an obstruction may need to be removed surgically.

Struvite stones usually need to be removed by endoscopic surgery. Antibiotics are not helpful for urinary tract infections until the stones are removed.

Last full review/revision August 2007 by Glenn M. Preminger, MD