A kidney stone is a solid mass made up of tiny crystals. One or more stones can be in the kidney or ureter at the same time.

See also: Cystinuria

Kidney stones can form when urine contains too much of certain substances. These substances can create small crystals that become stones.

The biggest risk factor for kidney stones is dehydration.

Kidney stones may not produce symptoms until they begin to move down the tubes (ureters) through which urine empties into the bladder. When this happens, the stones can block the flow of urine out of the kidneys. This causes swelling of the kidney or kidneys, causing pain. The pain is usually severe.

Kidney stones are common. A person who has had kidney stones often gets them again in the future. Kidney stones often occur in premature infants.

Some types of stones tend to run in families. Certain kinds of stones can occur with bowel disease, ileal bypass for obesity, or renal tubule defects.

There are different types of kidney stones. The exact cause depends on the type of stone.

• Calcium stones are most common. They occur more often in men than in women, and usually appear between ages 20 - 30. They are likely to come back. Calcium can 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 risk of forming calcium oxalate stones.
• Cystine stones can form in people who have cystinuria. This disorder runs in families and affects both men and women.
• Struvite stones are mostly found in women who have a urinary tract infection. These stones can grow very large and can block the kidney, ureter, or bladder.
• Uric acid stones are more common in men than in women. They can occur with gout or chemotherapy.

Other substances also can form stones.

The main symptom is severe pain that starts suddenly and may go away suddenly:

• Pain may be felt in the belly area or side of the back
• Pain may move to groin area (groin pain) or testicles (testicle pain)

Other symptoms can include:

• Abnormal urine color
• Blood in the urine
• Chills
• Fever
• Nausea
• Vomiting

Pain can be severe enough to need narcotic pain relievers. The belly area (abdomen) or back might feel tender to the touch.

Tests for kidney stones include:

• Analysis of the stone to show what type of stone it is
• Uric acid level
• Urinalysis to see crystals and red blood cells in urine

Stones or a blockage of the ureter can be seen on:

• Abdominal CT scan
• Abdominal/kidney MRI
• Abdominal x-rays
• Intravenous pyelogram (IVP)
• Kidney ultrasound
• Retrograde pyelogram

Tests may show high levels of calcium, oxylate, or uric acid in the urine or blood.

The goal of treatment is to relieve symptoms and prevent further symptoms. (Kidney stones that are small enough usually pass on their own.) Treatment varies depending on the type of stone and how severe the symptoms are. People with severe symptoms might need to be hospitalized.

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

Drink at least 6 - 8 glasses of water per day to produce a large amount of urine. Some people might need to get fluids through a vein (intravenous).

Pain relievers can help control the pain of passing the stones (renal colic). For severe pain, you may need to take narcotic pain killers or nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen.

Depending on the type of stone, your doctor may prescribe medicine to decrease stone formation or help break down and remove the material that is causing the stone. Medications can include:

• Allopurinol (for uric acid stones)
• Antibiotics (for struvite stones)
• Diuretics
• Phosphate solutions
• Sodium bicarbonate or sodium citrate (which make the urine more alkaline)

Surgery is usually needed if:

• The stone is too large to pass on its own
• The stone is growing
• The stone is blocking urine flow and cuasing an infection or kidney damage

Today, most treatments are much less invasive than in the past.

• Extracorporeal shock-wave lithotripsy is used to remove stones slightly smaller than a half an inch that are located near the kidney. This method uses ultrasonic waves or shock waves to break up stones. Then, the stones leave the body in the urine.
• Percutaneous nephrolithotomy is used for large stones in or near the kidney, or when the kidneys or surrounding areas are incorrectly formed. The stone is removed with an endoscope that is inserted into the kidney through a small opening.
• Ureteroscopy may be used for stones in the lower urinary tract.
• Standard open surgery (nephrolithotomy) may be needed if other methods do not work or are not possible.

Kidney stones are painful but usually can be removed from the body without causing permanent damage. They tend to return, especially if the cause is not found and treated.

• Decrease or loss of function in the affected kidney
• Kidney damage, scarring
• Obstruction of the ureter (acute unilateral obstructive uropathy)
• Recurrence of stones
• Urinary tract infection

Call your health care provider if you have symptoms of a kidney stone.

Also call if symptoms return, urination becomes painful, urine output decreases, or other new symptoms develop.

If you have a history of stones, drink plenty of fluids (6 - 8 glasses of water per day) to produce enough urine. Depending on the type of stone, you might need to take medications or other measures to prevent the stones from returning.

You may need to change your diet to prevent some types of stones from coming back.

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Finkielstein VA. Strategies for preventing calcium oxalate stones. CMAJ. 2006;174(10):1407-1409.

Pietrow PK, Preminger GM. Evaluation and medical management of urinary lithiasis. In: Wein AJ, ed. Campbell-Walsh Urology. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 43.