Kidney Stones

Overview 
Physician developed and monitored. 

Kidney stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles and develop into stones over time. The medical term for this condition is nephrolithiasis, or renal stone disease.

The kidneys filter waste products from the blood and add them to the urine that the kidneys produce. When waste materials in the urine do not dissolve completely, crystals and kidney stones are likely to form.

Small stones can cause some discomfort as they pass out of the body. Regardless of size, stones may pass out of the kidney, become lodged in the tube that carries urine from the kidney to the bladder (ureter), and cause severe pain that begins in the lower back and radiates to the side or groin. A lodged stone can block the flow of urine, causing pressure to build in the affected ureter and kidney. Increased pressure results in stretching and spasm, which cause severe pain.

Stone Formation

Kidney stones form when there is a high level of calcium (hypercalciuria), oxalate (hyperoxaluria), or uric acid (hyperuricosuria) in the urine; a lack of citrate in the urine; or insufficient water in the kidneys to dissolve waste products. The kidneys must maintain an adequate amount of water in the body to remove waste products. If dehydration occurs, high levels of substances that do not dissolve completely (e.g., calcium, oxalate, uric acid) may form crystals that slowly build up into kidney stones.

Urine normally contains chemicals—citrate, magnesium, pyrophosphate—that prevent the formation of crystals. Low levels of these inhibitors can contribute to the formation of kidney stones. Of these, citrate is thought to be the most important.

Types

What Are Kidney Stones?

The chemical composition of stones depends on the chemical imbalance in the urine. The four most common types of stones are comprised of calcium, uric acid, struvite, and cystine.

Calcium Stones Approximately 85% of stones are composed predominantly of calcium compounds. The most common cause of calcium stone production is excess calcium in the urine (hypercalciuria). Excess calcium is normally removed from the blood by the kidneys and excreted in the urine. In hypercalciuria, excess calcium builds up in the kidneys and urine, where it combines with other waste products to form stones. Low levels of citrate, high levels of oxalate and uric acid, and inadequate urinary volume may also cause calcium stone formation.

Calcium stones are composed of calcium that is chemically bound to oxalate (calcium oxalate) or phosphate (calcium phosphate). Of these, calcium oxalate is more common. Calcium phosphate stones typically occur in patients with metabolic or hormonal disorders such as hyperparathyroidism and renal tubular acidosis.

Increased intestinal absorption of calcium (absorptive hypercalciuria), excessive hormone levels (hyperparathyroidism), and renal calcium leak (kidney defect that causes excessive calcium to enter the urine) can cause hypercalciuria. Prolonged inactivity also increases urinary calcium and may cause stones.

Renal tubular acidosis (inherited condition in which the kidneys are unable to excrete acid) significantly reduces urinary citrate and total acid levels and can lead to stone formation, usually calcium phosphate.

Uric Acid StonesDigestion produces uric acid. If the acid level in the urine is high or too much acid is excreted, the uric acid may not dissolve and uric acid stones may form. Genetics may play a role in the development of uric acid stones, which are more common in men. Approximately 10% of patients with kidney stone disease develop this type of stone.

Struvite StonesThis type of stone, also called an infection stone, develops when a urinary tract infection (e.g., bladder infection) affects the chemical balance of the urine. Bacteria in the urinary tract release chemicals that neutralize acid in the urine, which enables bacteria to grow more quickly and promotes struvite stone development.

Struvite stones are more common in women because they have urinary tract infections more often. The stones usually develop as jagged structures called "staghorns" and can grow to be quite large.

Cystine StonesCystine is an amino acid in protein that does not dissolve well. Some people inherit a rare, congenital (i.e., present at birth) condition that results in large amounts of cystine in the urine. This condition (called cystinuria) causes cystine stones that are difficult to treat and requires life-long therapy.

Incidence and Prevalence 
People who live near large bodies of water (e.g., Great Lakes, Gulf of Mexico), those who live in "soft" water areas, and those who have a sibling or parent with the condition experience a higher incidence of renal stone disease. According to the U.S. National Institutes of Health, 1 person in 10 develops kidney stones during their lifetime and renal stone disease accounts for 7–10 of every 1000 hospital admissions. Kidney stones are most prevalent in patients between the ages of 30 and 45, and the incidence declines after age 50.

 

When should I call a doctor?

Pain in the shaded areas may be caused by a kidney stone.
If you have a kidney stone, you may already know how painful it can be. Most kidney stones pass out of the body without help from a doctor. But sometimes a stone will not pass. It may even get larger. Your doctor can help.

You should call a doctor if you have any of the following signs:
•    extreme pain in your back or side that will not go away 
•    blood in your urine 
•    fever and chills 
•    vomiting 
•    urine that smells bad or looks cloudy 
•    a burning feeling when you urinate 

These may be signs of a kidney stone that needs a doctor’s care.

What do my kidneys do?
Your kidneys are bean-shaped organs, each about the size of your fist. They are located near the middle of your back, just below the rib cage, one on each side of the spine. The kidneys are sophisticated trash collectors. Every day, your kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The wastes and extra water become urine, which flows to your bladder through tubes called ureters. Your bladder stores urine until you go to the bathroom.

Wastes removed from the blood go to the bladder.
The wastes in your blood come from the normal breakdown of active muscle and from the food you eat. Your body uses the food for energy and self-repair. After your body has taken what it needs from the food, wastes are sent to the blood. If your kidneys did not remove these wastes, they would build up in the blood and damage your body.
In addition to removing wastes, your kidneys help control blood pressure. They also help make red blood cells and keep your bones strong.

What is a kidney stone?
A kidney stone is a solid piece of material that forms in a kidney out of substances in the urine.
A stone may stay in the kidney or break loose and travel down the urinary tract. A small stone may pass all the way out of the body without causing too much pain.
A larger stone may get stuck in a ureter, the bladder, or the urethra. A problem stone can block the flow of urine and cause great pain.

Are all kidney stones alike?
No. Doctors have found four major types of kidney stones.
•    The most common type of stone contains calcium. Calcium is a normal part of a healthy diet.
Calcium that is not used by the bones and muscles goes to the kidneys. In most people, the kidneys flush out the extra calcium with the rest of the urine. People who have calcium stones keep the calcium in their kidneys.
The calcium that stays behind joins with other waste products to form a stone. The most common combination is called calcium oxalate.
•    A struvite stone may form after an infection in the urinary system. These stones contain the mineral magnesium and the waste product ammonia.
•    A uric acid stone may form when the urine contains too much acid. If you tend to form uric acid stones, you may need to cut back on the amount of meat you eat.
•    Cystine stones are rare. Cystine is one of the building blocks that make up muscles, nerves, and other parts of the body. Cystine can build up in the urine to form a stone. The disease that causes cystine stones runs in families.

What do kidney stones look like?
Kidney stones may be as small as a grain of sand or as large as a pearl. Some stones are even as big as golf balls. Stones may be smooth or jagged. They are usually yellow or brown.

Golf-ball-sized and brown    Jagged and yellow    Small and smooth
________________________________________
Kidney stones vary in size and shape. These are not actual size.


What can my doctor do about a problem stone?

If you have a stone that will not pass by itself, your doctor may need to take steps to get rid of it. In the past, the only way to remove a problem stone was through surgery.
Now, doctors have new ways to remove problem stones. The following sections describe a few of these methods.

Shock Waves
Your doctor can use a machine to send shock waves directly to the kidney stone. The shock waves break a large stone into small stones that will pass through your urinary system with your urine. The full name for this method is extracorporeal shock wave lithotripsy. Doctors often call it ESWL for short. Lithotripsy is a Greek word that means stone crushing.

Two types of shock wave machines exist. With one machine, you sit in a tub of water. With most newer machines, you lie on a table. A health technician will use ultrasound or x-ray images to direct the sound waves to the stone.

Tunnel Surgery
In tunnel surgery, the doctor makes a small cut into the patient’s back and makes a narrow tunnel through the skin to the stone inside the kidney. With a special instrument that goes through the tunnel, the doctor can find the stone and remove it. The technical name for this method is percutaneous nephrolithotomy.

Ureteroscope
A ureteroscope looks like a long wire. The doctor inserts it into the patient’s urethra, passes it up through the bladder, and directs it to the ureter where the stone is located. The ureteroscope has a camera that allows the doctor to see the stone. A cage is used to catch the stone and pull it out, or the doctor may destroy it with a device inserted through the ureteroscope.
Ask your doctor which method is right for you.


How will my doctor find out what kind of stone I have?
Try to catch a stone in a strainer.
The best way for your doctor to find out what kind of stone you have is to test the stone itself. If you know that you are passing a stone, try to catch it in a strainer.
Your doctor may ask for a urine sample or take blood to find out what caused your stone. You may need to collect your urine for a 24-hour period. These tests will help your doctor find ways for you to avoid stones in the future.

Why do I need to know the kind of stone?
The therapy your doctor gives you depends on the type of stone you have. For example, a medicine that helps prevent calcium stones will not work if you have a struvite stone. The diet changes that help prevent uric acid stones may not work to prevent calcium stones. Therefore, careful analysis of the stone will help guide your treatment.

What can I do to avoid more stones?
Drink more water. Try to drink 12 full glasses of water a day. Drinking lots of water helps to flush away the substances that form stones in the kidneys.
You can also drink ginger ale, lemon-lime sodas, and fruit juices. But water is best. Limit your coffee, tea, and cola to 1 or 2 cups a day because the caffeine may cause you to lose fluid too quickly.

Try to drink 12 full glasses of water every day.
Your doctor may ask you to eat more of some foods and to cut back on other foods. For example, if you have a uric acid stone, your doctor may ask you to eat less meat, because meat breaks down to make uric acid.
If you are prone to forming calcium oxalate stones, you may need to limit foods that are high in oxalate. These foods include rhubarb, beets, spinach, and chocolate.
The doctor may give you medicines to prevent calcium and uric acid stones.

Points to Remember
•    Most stones will pass out of the body without a doctor’s help. 
•    See your doctor if you have severe pain in your back or side that will not go away. 
•    See your doctor if you have blood in your urine—urine will appear pink. 
•    When you pass a stone, try to catch it in a strainer to show your doctor. 
•    Drink lots of water to prevent more kidney stones from forming. 
•    Talk with your doctor about other ways to avoid more stones.

ADDITIONAL INFORMATION:

What I need to know about Kidney Stones
On this page:
•    When should I call a doctor? 
•    What do my kidneys do? 
•    What is a kidney stone? 
•    Are all kidney stones alike? 
•    What do kidney stones look like? 
•    What can my doctor do about a problem stone? 
•    How will my doctor find out what kind of stone I have? 
•    Why do I need to know the kind of stone? 
•    What can I do to avoid more stones? 
•    Points to Remember 
•    For More Information 
•    Acknowledgments


Points to Remember
•    Most stones will pass out of the body without a doctor’s help. 
•    See your doctor if you have severe pain in your back or side that will not go away. 
•    See your doctor if you have blood in your urine—urine will appear pink. 
•    When you pass a stone, try to catch it in a strainer to show your doctor. 
•    Drink lots of water to prevent more kidney stones from forming. 
•    Talk with your doctor about other ways to avoid more stones. 

For More Information
American Urological Association Foundation
1000 Corporate Boulevard, Suite 410
Linthicum, MD 21090
Phone: 1–866–RING–AUA (746–4282)
Email: patienteducation@auafoundation.org
Internet: www.auafoundation.org
www.UrologyHealth.org

National Kidney Foundation, Inc.
30 East 33rd Street
New York, NY 10016
Phone: 1–800–622–9010 or 212–889–2210
Internet: www.kidney.org

Oxalosis and Hyperoxaluria Foundation
201 East 19th Street, Suite 12E
New York, NY 10003
Phone: 1–800–OHF–8699 (643–8699) or 212–777–0470
Fax: 212–777–0471
Email: execdirector@ohf.org
Internet: www.ohf.org