Urological Disorders

Kidney Stones

What is a kidney stone?

A kidney stone is a solid piece of material that forms out of substances in the urine in the kidney. The stone may remain in the kidney or break loose and travel down the urinary tract. A small stone may pass all of the way out of the body, but a larger stone can get stuck in a ureter, the bladder, or the urethra. This may block the flow of urine and cause great pain.

A kidney stone may be as small as a grain of sand or as large as a pearl, and some are as big as golf balls. They may be smooth or jagged, and are usually yellow or brown.

Who is often affected by kidney stones?

Kidney stones are one of the most painful disorders to afflict humans, and one of the most common disorders of the urinary tract. It is estimated that 10 percent of all people in the United States will have a kidney stone at some point in time. Caucasians are more prone to kidney stones than are African-Americans. Although stones occur more frequently in men, the number of women who get kidney stones has been increasing. Kidney stones strike most people between the ages of 20 and 40. Once a person gets more than one stone, he or she is more likely to develop others.

What are some of the types of kidney stones?

A kidney stone develops from crystals that separate from urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent or inhibit the crystals from forming, however, in some people, stones still become formed. Crystals that remain small enough will travel through the urinary tract and pass out of the body in the urine without even being noticed.

Calcium is the most common type of stone. Calcium is a normal part of a healthy diet and is used by bones and muscles. Calcium not used by the body goes to the kidneys where is normally flushed out with the rest of the urine. In some people, however, the calcium that stays behind joins with other waste products to form a stone.

Struvite is a type of stone that contains the mineral magnesium and the waste product ammonia. It may form after an infection in the urinary system.

Uric acid stones may form when there is too much acid in the urine.

Cystine, one of the building blocks that make up muscles, nerves, and other parts of the body, can build up in the urine and form a stone. Cystine stones are rare. The disease that causes cystine stones often runs in families.

What are symptoms of kidney stones?

The first symptom of a kidney stone usually is extreme pain. It may begin suddenly as a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain in the back and side around the area of the kidney, or in the lower abdomen. The pain may spread to the groin. Sometimes nausea and vomiting occur.

When the stone is too large to pass easily, the pain continues as the muscles in the wall of the tiny ureter try to squeeze the stone along into the bladder. As a stone grows or moves, blood may be found in the urine. As the stone moves down the ureter closer to the bladder, a person may feel the need to urinate more often or feel a burning sensation during urination. The following may be signs of a kidney stone:

extreme pain in the back or side that will not go away
blood in the urine
fever and chills
vomiting
urine that smells bad or looks cloudy
a burning feeling when you urinate

If these symptoms occur, see your physician as soon as possible.

How kidney stones may be diagnosed:
"Silent" stones, those that cause no symptoms, are usually found on x-rays during a general health exam. These stones are likely to pass without being noticed.

More often, kidney stones are found on an x-ray or sonogram taken on someone who complains of blood in the urine or sudden pain. Diagnostic images give information about the stone's size and location. Blood and urine tests also help detect any abnormal substance that might promote stone formation.

An IVP (intravenous pyelogram) scan, a special x-ray test, of the urinary system may be used.

How kidney stones may be treated:
Some kidney stones pass out of the body without any intervention by a physician. In cases that cause lasting symptoms or other complications, kidney stones may be treated by various techniques, depending upon your physician's recommendation, your medical profile, and the severity of the condition. The following treatments may be considered:

shock waves - extracorporeal shock wave lithotripsy (ESWL) - use of a machine to send shock waves directly to the kidney stone to break a large stone into smaller stones that will pass through the urinary system with your urine. There are two types of shock wave machines: with one machine, the patient sits in a tub of water, with the other, the patient lies on a table.

tunnel surgery - percutaneous nephrolithotomy - a small cut is made in the patient's back and a narrow tunnel is made through the skin to the stone inside the kidney. A special instrument goes through this tunnel allowing the doctor to locate and remove the stone.

ureteroscope - a long wire with a camera attached to it is inserted it into the patient's urethra and passed up through the bladder to the ureter where the stone is located. A cage is used to retrieve the stone and remove it from the body.

How development of future kidney stones may be prevented:
According to the National Kidney and Urologic Diseases Foundation, the best ways to avoid getting kidney stones is the following:

Drink more water -- up to 12 full glasses of water a day can help to flush away the substances that form stones in the kidneys. Ginger ale, lemon-lime sodas, and fruit juices are acceptable, but water is best.
Limit coffee, tea, and cola to one or two cups a day. The caffeine may cause a rapid loss of fluid.
Consult your physician regarding dietary modifications.
Medications may be prescribed to prevent calcium and uric acid stones.

This page was last updated on: February 28, 2008.

For more information, call the University Physicians Consultation and Referral Service at 1-800-492-5538 (patients) or 1-800-373-4111 (physicians).