Tiny stones may cause no symptoms, but larger stones can cause excruciating pain in the area between the ribs and hips in the back.
Usually, an imaging test and an analysis of urine are done to diagnose stones.
Sometimes stone formation can be prevented by changing the diet or increasing fluid intake.
Stones that do not pass on their own are removed with lithotripsy Stone removal 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. Tiny stones may cause no symptoms, but larger stones... read more (the use of shock waves to break up those stones) or an endoscopic technique (the use of specialized tools to view and operate on internal organs).
Urinary tract stones begin to form in a kidney and may enlarge in 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
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 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
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 ) 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.
Stones are more common among people with certain disorders (for example, hyperparathyroidism Hyperparathyroidism In hypercalcemia, the level of calcium in blood is too high. A high calcium level may result from a problem with the parathyroid glands, as well as from diet, cancer, or disorders affecting... read more , dehydration Dehydration Dehydration is a deficiency of water in the body. Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration. People feel thirsty, and as dehydration... read more , and renal tubular acidosis Renal Tubular Acidosis (RTA) In renal tubular acidosis, the kidney tubules malfunction, resulting in excess levels of acid in the blood. The tubules of the kidneys that remove acid from the blood are damaged when a person... read more ) and among people whose diet is very high in animal-source 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. People who have undergone surgery for weight loss (bariatric surgery) may also be at increased risk of stone formation.
Rarely, drugs (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
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
Peritonitis, which may be caused by 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 , ectopic pregnancy Ectopic Pregnancy Ectopic pregnancy is attachment (implantation) of a fertilized egg in an abnormal location. In an ectopic pregnancy, the fetus cannot survive. When an ectopic pregnancy ruptures, women often... read more , or pelvic inflammatory disease Pelvic Inflammatory Disease (PID) Pelvic inflammatory disease is an infection of the upper female reproductive organs (the cervix, uterus, fallopian tubes, and ovaries). Pelvic inflammatory disease is usually transmitted during... read more
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 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...
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 only show 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 This chapter includes a new section on COVID-19 and acute kidney injury (AKI). Kidney failure is the inability of the kidneys to adequately filter metabolic waste products from the blood. Kidney... read more ). Doctors rarely use excretory urography to diagnose stones if CT or ultrasonography is available.
Urinalysis Urinalysis and Urine Culture Urinalysis, the testing of urine, may be necessary in the evaluation of kidney and urinary tract disorders and can also help evaluate bodywide disorders such as diabetes or liver problems. A... read more is usually done. It may show blood or pus in the urine whether or not symptoms are present.
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.
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.
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...
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.
In rare cases, when calcium stones result from hyperparathyroidism Hyperparathyroidism In hypercalcemia, the level of calcium in blood is too high. A high calcium level may result from a problem with the parathyroid glands, as well as from diet, cancer, or disorders affecting... read more , sarcoidosis Sarcoidosis Sarcoidosis is a disease in which abnormal collections of inflammatory cells (granulomas) form in many organs of the body. Sarcoidosis usually develops in people aged 20 to 40, most often people... read more , vitamin D toxicity Vitamin D Excess Taking very high doses of vitamin D supplements can cause vitamin D toxicity. Vitamin D toxicity causes high levels of calcium in the blood. People with vitamin D toxicity may lose their appetite... read more , renal tubular acidosis Renal Tubular Acidosis (RTA) In renal tubular acidosis, the kidney tubules malfunction, resulting in excess levels of acid in the blood. The tubules of the kidneys that remove acid from the blood are damaged when a person... read more , or cancer, the underlying disorder must be treated.
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.
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.
People with recurrent struvite stones may need to take antibiotics continually to prevent urinary tract infections 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 . Acetohydroxamic acid may also be helpful in people with struvite stones.
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. Some drugs (tamsulosin or calcium channel blockers) may increase the likelihood of spontaneous stone passage.
The pain of renal colic may be relieved with NSAIDs. If the pain is severe, opioids are sometimes needed.
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.
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).
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. 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. Sometimes, a laser is used to break up the stone. When a laser is used, the procedure is called holmium laser lithotripsy.
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.
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.