What Are They?
Kidney stones are abnormal, hard, chemical deposits that form inside the kidneys. This condition also is called nephrolithiasis or urolithiasis. Kidney stones are often as small as grains of sand and pass out of the body in urine without causing discomfort. The deposits can be the size of a pea, a marble or even larger. Some of these larger stones are too big to be flushed from the kidney. Others manage to travel into the narrow tube between the kidney and bladder (ureter), where they become trapped. Trapped kidney stones can cause many different symptoms, including extreme pain, blocked urine flow and bleeding from the walls of the urinary tract.
Kidney stones are a very common problem, affecting 10% of people in the United States. There are several different types of stones, and a variety of reasons why stones form. Doctors have grouped kidney stones into four different families, based on their chemical composition:
Calcium oxalate stones — These stones account for more than 75% of all kidney stones. They are more common in men than in women, and they are more common in adults than in children. In 50% of people with calcium stones, the stones form because of an increased level of calcium in the urine, which probably is inherited (genetic). In other people, calcium oxalate stones are caused by another condition such as extra parathyroid hormone, high uric acid levels (as in people who have gout), bowel disease, surgery for obesity, or kidney problems.
Struvite stones — These stones are made of magnesium and ammonia (a waste product), and are related to urinary tract infections caused by certain bacteria. Struvite stones used to account for 10% to 15% of all kidney stones, but they are less common now that urinary tract infections are better recognized and treated. Struvite stones are more common in women than in men, and they develop frequently in people who have long-term bladder catheters.
Uric acid stones — These stones account for 5% to 8% of all kidney stones, and are more common in men than in women. Uric acid stones form because of an abnormally high concentration of uric acid in the urine. They often occur in people who have gout, a disorder in which uric acid builds up in the blood and joints.
Cystine stones — These rare stones account for less than 1% of kidney stones. They are composed of the amino acid cystine, which is a building block of proteins, and they are caused by an inherited (genetic) defect.
Very small kidney stones may pass out of the body in the urine without causing symptoms. Larger stones may become trapped in the narrow ureter, causing severe pain in the back or side, nausea and vomiting, or blood in the urine. If there is blood in your urine, it will look pink or red. If the location of pain shifts downward, closer to the groin, this usually indicates that the stone has traveled downward in the ureter and is now closer to the bladder. As the stone approaches the bladder, there may be an increased urge to urinate or a burning sensation when urinating. When stones pass out of your body in your urine, you may see the stones exit.
Your doctor will ask you about your symptoms and about any change in the color of your urine. He or she will ask about your family history of kidney stones, and whether you have had gout.
If you are in extreme pain, your doctor can use X-rays, computed tomography (CT) scans or ultrasound to look for a kidney stone and see if it is trapped. If you are able to collect a stone that you passed from your urine, your doctor will send the stone to a laboratory for chemical analysis. Blood and urine tests may be done to identify a treatable cause of the stone.
If you do not have any symptoms and you find a small kidney stone in your urine, strain out the stone and save it for your doctor. Your doctor can send the stone to a medical laboratory for chemical analysis.
When a kidney stone becomes trapped in the ureter, it may remain there until your doctor removes it, or it eventually may move downward and pass on its own. It can take hours, days or weeks for a stone to pass. As a rule, the smaller the stone, the more likely it is to pass on its own. The larger the stone, the greater the risk that it will remain trapped in the ureter, significantly obstructing the flow of urine and eventually causing infection.
In general, you can help to prevent kidney stones by drinking plenty of fluids and avoiding dehydration. This dilutes your urine and decreases the chance that chemicals will combine to form stones.
You can prevent calcium oxalate stones by eating low-fat dairy products and other calcium-rich foods. Taking calcium supplements, however, can increase the risk of stone formation. Calcium in your diet binds oxalate inside the intestines to decrease the amount of oxalate that gets into the blood, so less spills in the urine. People who excrete too much oxalate into their urine should avoid eating foods high in oxalate, including beets, spinach, chard and rhubarb. Tea, coffee, cola, chocolate and nuts also contain oxalate, but these can be used in moderation. Eating too much salt and meat can cause more kidney stones to form.
After your doctor receives an analysis of the chemical composition of your kidney stones, he or she can suggest medications or changes in your diet that will help to prevent stones from forming in the future. Because certain medications may increase the risk of stones, your doctor may want to adjust your regular medications if you have had kidney stones.
In many cases, a trapped kidney stone eventually flushes out of the urinary tract on its own, especially if you drink plenty of fluids. With a doctor's supervision, it is likely that you can remain at home, taking pain medicine as needed until the stone dislodges and flushes away. If the stone is too large to pass on its own, if your pain is severe, or if you have infection or significant bleeding, it may be necessary for you to have your stone removed or broken into fragments that can pass more easily. Doctors have several options for destroying stones lodged in the urinary tract:
Extracorporeal lithotripsy — Shock waves applied externally break kidney stones into smaller fragments, which are then swept away in the urine stream.
Percutaneous ultrasonic lithotripsy — A narrow tubelike instrument is passed through a small incision in the back to the kidney, where ultrasound breaks up the kidney stones. The stone fragments are then removed.
Laser lithotripsy — A laser breaks up stones in the ureter. The stones then pass on their own.
Ureteroscopy — A very small telescope is inserted into the ureter and guided to the bladder. The stone is then either fragmented or removed.
It is rare that surgery is required to remove a kidney stone.
Once a kidney stone has been removed, you can sometimes prevent new stones from forming with medications or changes in diet. For example, thiazide diuretic medications may be prescribed for some people with calcium stones, while some people with uric acid stones may be treated with allopurinol (Aloprim, Zyloprim).
When To Call A Professional
Call your doctor whenever you have:
Severe pain in your back or side, with or without nausea and vomiting
Unusually frequent urination or a persistent urge to urinate
A burning and discomfort when urinating
Urine that is colored pink or tinged with blood
Because trapped kidney stones can lead to a urinary tract infection, call your doctor if you have fever and chills, or if your urine becomes cloudy or foul smelling.
The prognosis varies from person to person, depending on the cause of the kidney stones and on the willingness of the person to take medications or make lifestyle changes. Up to half of people who pass a kidney stone will never pass a second.
National Institute of Diabetes and Digestive and Kidney Disorders
Office of Communications and Public Liaison
Building 31, Room 9A04
Center Drive, MSC 2560
Bethesda, MD 20892-2560
Phone: (301) 496-3583
Fax: (301) 496-7422
American Foundation for Urologic Disease
1000 Corporate Blvd., Suite 410
Linthicum, MD 21090
Phone: (410) 689-3990
Toll-Free: (800) 828-7866
Fax: (410) 689-3998
National Kidney Foundation
30 East 33rd St.
New York, NY 10016
Phone: (212) 889-2210
Toll-Free: (800) 622-9010
Fax: (212) 689-9261
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