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Kidney stones


A kidney stone is a solid mass that consists of a collection of tiny crystals. There can be one or more stones present at the same time in the kidney or in the ureter. (See also cystinuria.)

Causes, incidence, and risk factors

Kidney stones may form when your urine becomes too concentrated with certain substances. These substances may create small crystals that become stones. The kidney stones may not produce symptoms until they begin to move down the ureter, causing pain. The pain is usually severe and often starts in the flank region, then moves down to the groin.

Kidney stones are common. About 5% of women and 10% of men will have at least one episode by age 70. A person who has had kidney stones often gets them again in the future. Kidney stones are common in premature infants.

Other risk factors include renal tubular acidosis and resultant nephrocalcinosis.

Some types of stones tend to run in families. Some types may be associated with bowel disease, ileal bypass for obesity, or renal tubule defects.

Types of stones include:

  • Calcium stones are most common. They are two to three times more common in men, usually appearing at age 20 to 30. Recurrence is likely. The calcium may combine with other substances such as oxalate (the most common substance), phosphate, or carbonate to form the stone. Oxalate is present in certain foods. Diseases of the small intestine increase the tendency to form calcium oxalate stones.
  • Uric acid stones are also more common in men. They are associated with gout or chemotherapy. Uric acid stones make up about 10% of all stones.
  • Cystine stones may form in persons with cystinuria. It is a hereditary disorder affecting both men and women.
  • Struvite stones are mainly found in women as a result of urinary tract infection. They can grow very large and may obstruct the kidney, ureter, or bladder.

Other substances may crystallize, precipitate, and form stones.


Signs and tests

Pain may be severe enough to require narcotics. There may be tenderness when the abdomen or back is touched. If stones are severe, persistent, or come back again and again, there may be signs of kidney failure.

Stones or obstruction of the ureter may be seen on:

Tests may reveal high levels of calcium in the blood or urine.


The goal of treatment is to relieve symptoms and prevent further symptoms. (Kidney stones usually pass on their own.) Treatment varies depending on the type of stone and the extent of symptoms or complications. Hospitalization may be required if the symptoms are severe.

When the stone passes, the urine should be strained and the stone saved for analysis to determine the type.

Drink enough fluids to produce a high urinary output. Water is encouraged, at least 6 to 8 glasses per day. Intravenous fluids may be required.

Pain relievers may be needed to control renal colic (pain associated with the passage of stones). Severe pain may require narcotic analgesics.

Depending on the type of stone, medications may be given to decrease stone formation and/or aid in the breakdown and excretion of the material causing the stone. These may include such medications as diuretics, phosphate solutions, allopurinol (for uric acid stones), antibiotics (for struvite stones), and medications that alkalinize the urine such as sodium bicarbonate or sodium citrate.

If the stone is not passed on its own, surgical removal may be required. Lithotripsy may be an alternative to surgery. Ultrasonic waves or shock waves are used to break up stones so that they may be expelled in the urine (extracorporeal shock-wave lithotripsy) or removed with an endoscope that is inserted into the kidney via a small flank incision (percutaneous nephrolithotomy).

You may need to modify your diet to prevent some types of stones from returning.

Expectations (prognosis)

Kidney stones are painful but usually are excreted without causing permanent damage. They tend to return, especially if the underlying cause is not found and treated.


Calling your health care provider

Call your health care provider if symptoms indicate a kidney stone may be present.

Also call if symptoms of kidney stone recur, urination becomes painful, urine output decreases, or other new symptoms develop.


If there is a history of stones, fluids should be encouraged to produce adequate amounts of dilute urine (usually 6 to 8 glasses of water per day). Depending on the type of stone, medications or other measures may be recommended to prevent recurrence.


Kidney anatomy
Kidney anatomy
Kidney - blood and urine flow
Kidney - blood and urine flow
Intravenous pyelogram (IVP)
Intravenous pyelogram (IVP)
Lithotripsy procedure
Lithotripsy procedure

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