Medications — Some medications that promote formation of urine crystals increase the risk of stone formation. Excessive intake of vitamin C (more than 2 grams per day) can promote calcium oxalate stone formation. In addition, use of Vitamin D or calcium supplements may increase the risk of kidney stones in susceptible individuals by raising the level of calcium in the urine.

Diarrhea and dehydration— Uric acid stones are sometimes seen in patients who have chronic diarrhea, since such patients can have concentrated, acidic urine. People who are predisposed to developing stones have an increased risk of stone formation if they become dehydrated. This includes patients who engage in heavy physical exercise (such as marathon running).

SYMPTOMS — Symptoms of a kidney stone are the result of stone passage from the kidney into the ureter (the tube that leads from the kidney to the bladder). Pain, blood in the urine (hematuria), passing small stones in the urine ("gravel"), nausea or vomiting, and the urgent need to urinate are common symptoms of kidney stones.

Pain — Pain is the most common symptom and can range from a mild and barely noticeable ache, to discomfort that is so intense that it requires hospitalization for pain control. Pain occurs if the stone moves into the ureter, and is thought to be caused by stretching of the tissues surrounding the kidney due to blockage of urine flow.

Typically, the pain waxes and wanes in severity. Waves of severe pain, known as renal colic, usually last 20 to 60 minutes, although less severe pain can be present between episodes of renal colic.

Pain occurs on the side of the body where the stone is located. The area that is painful depends upon the location of the stone, which may change as the stone moves. A stone that obstructs the upper ureter or renal pelvis leads to flank pain (pain in the side, between the ribs and the hip) or tenderness. A stone that obstructs the lower portion of the ureter causes pain in the lower abdomen, which can spread to the genital area.

Hematuria — Hematuria (blood in the urine) occurs in most patients with kidney stones. The blood may be visible to the patient as pink or reddish urine, or may be visible only by urine dipstick testing or microscopic examination of the urine. (See "Patient information: Blood in the urine (hematuria)").

Gravel — Patients may pass "gravel" or small stones. Uric acid stones, in particular, are more likely to cause gravel and can also cause obstruction.

Other symptoms — Other symptoms include nausea or vomiting, pain with urination, and an urgent need to urinate (urgency). In some patients, the stone becomes stuck in the ureter, leading to persistent obstruction and possible infection.

Staghorn calculi are irregularly shaped stones with protruding branches. These stones have grown to fill all or part of the renal pelvis, and are too large to pass through the ureters. Infection or obstruction from these large stones may lead to kidney damage if they are not removed.

Asymptomatic kidney stones — Many patients with kidney stones have no symptoms (asymptomatic means without symptoms). These stones may be found when an imaging study (such as an ultrasound, x-ray or CT scan) is performed in a person with a prior history of stones, or when such a study is done for other purposes. Asymptomatic patients can remain symptom-free for years, although those with a history of stones are more likely to develop symptoms.

DIAGNOSIS — Clinical symptoms, laboratory tests, and imaging studies may be used to diagnose a kidney stone. A sudden onset of flank pain and hematuria (blood in the urine) are particularly suggestive of a kidney stone. Analysis of a urine sample should be performed to determine if blood or stone crystals are present. An imaging test is typically performed to confirm the presence of a stone and to rule out other conditions, especially if the patient has no previous history of stones. Computed tomography (CT scan) is the preferred diagnostic test in most patients.

Computed tomography (CT) scan — A CT scan creates a three dimensional image of structures within the body. A particular type of CT scan (called noncontrast helical CT) can visualize almost all kidney stones (including those that are not seen with the other imaging tests), and can determine if there is obstruction to urine flow within the urinary tract. This test is the best one for determining if a kidney stone is present, although it may not be necessary if a stone has been detected by another test.

Ultrasonography — Ultrasonography (the use of sound waves to visualize body structures) can also be used to detect stones, although small stones may be missed. It is the procedure of choice for patients who should avoid radiation, including pregnant women.

Abdominal x-ray — Many types of kidney stones can be seen on standard abdominal x-ray (called KUB, kidneys, ureter, bladder). However, certain stones, such as uric acid stones and small stones, may not be seen. As a result, another test, such as a CT scan, may be required if a kidney stone is likely but the abdominal x-ray is negative.

Intravenous pyelogram (IVP) — In an IVP, a radiopaque dye (one that is seen on x-ray) is injected into a vein. The dye collects in, and is excreted by, the kidneys. As the dye passes through the kidney and into the bladder, the urinary tract and any kidney stones are visible on x-ray. Although most kidney stones can often be detected by IVP, there is a small risk of reaction to the dye.

TREATMENT — Initial treatment for symptomatic kidney stones is similar for all patients. However, measures to prevent future stones vary depending upon a person's risk of recurrence.

Initial treatment — During the initial phase of kidney stone symptoms, many patients require only pain medication and fluids until the stone is passed. Nonsteroidal antiinflammatory drugs (NSAIDs, such as ibuprofen [Advil, Motrin] or naproxen [Aleve]) may be prescribed for pain and can be given by mouth. Intravenous NSAIDs (ketorolac [Toradol]) may be given into a vein if the patient is too nauseous to tolerate pills. If the pain is not controlled by an NSAID, narcotics (such as morphine) may be given. Fluids are recommended (either by mouth or in a vein) to increase urine flow and facilitate passage of the stone. Other medications, such as nifedipine (Procardia®) or tamsulosin (Flomax®), may also be recommended to further facilitate the passage of ureteral stones.

Patients who are able to take oral medications and fluids are usually managed at home. However, hospitalization may be required if the pain is severe or if the patient cannot tolerate oral fluids.

Patients are often asked to strain their urine to recover the stone; it can then be analyzed in a laboratory to determine its content. Once the stone is passed, an imaging test is sometimes performed to confirm that passage is complete and that no fragments or additional stones remain. Stones smaller than 5 millimeters, and even those up to 9 or 10 millimeters, often pass on their own without requiring a procedure.

If the stone does not pass — Stones larger than 9 or 10 millimeters rarely pass on their own and generally require treatment. Several procedures are available.

Shock wave lithotripsy (SWL) — SWL is the treatment of choice in many patients who need help passing a stone, and is particularly good for stones in the renal pelvis and upper ureter. SWL requires an x-ray or ultrasound to pinpoint the location of the stone. A high energy shock wave is then directed toward the stone, passing through the skin and bodily tissues and causing a release of energy at the stone surface. This energy causes the stone to break into fragments that can be more easily passed. SWL therapy may not be effective for treating large, hard, or complex stones (such as staghorn calculi).

Percutaneous nephrolithotomy (PNL) — Extremely large or complex stones, or stones resistant to shock wave lithotripsy, may require a surgical procedure to remove the stone. In this procedure, small telescopic instruments are passed through the skin (percutaneously) into the kidney to remove the stone.

Ureteroscopy — Ureteroscopy is often used to remove stones obstructing the middle and lower portion of the ureter. In this procedure, a very small telescopic instrument is passed through the urethra and bladder, into the ureter and kidney. This scope contains a camera and other instruments, which allows the physician to visualize the obstructing stone and remove it, or to break it up into smaller pieces that can pass more easily.

Treatment of asymptomatic stones — Patients with asymptomatic stones may be treated, depending upon the size and location of the stone. Other factors are considered in deciding whether to treat the stone, including the patient's occupation (eg, pilot, frequent traveler, local worker) and their ability to easily receive treatment. Patients who might have difficulty receiving prompt treatment are more likely to be treated before they develop symptoms.