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Kidney stones, one of the most painful of the urologic disorders,
are not a product of modern life. Scientists have found evidence of
kidney stones in a 7,000-year-old Egyptian mummy. Unfortunately,
kidney stones are one of the most common disorders of the urinary
tract; patients made more than 1.3 million visits to health care
providers to have their stones treated in 1997. In 1999, more than a
quarter million hospitalized patients had a diagnosis of kidney
stones. An estimated 10 percent of people in the United States will
have a kidney stone at some point in their lives. Men tend to be
affected more frequently than women.
Most kidney stones pass out of the body without any intervention
by a physician. Stones that cause lasting symptoms or other
complications may be treated by various techniques, most of which do
not involve major surgery. Also, research advances have led to a
better understanding of the many factors that promote stone
The urinary tract
The urinary tract, or system, consists of the kidneys, ureters,
bladder, and urethra. The kidneys are two bean-shaped organs located
below the ribs toward the middle of the back. The kidneys remove
extra water and wastes from the blood, converting it to urine. They
also keep a stable balance of salts and other substances in the
blood. The kidneys produce hormones that help build strong bones and
help form red blood cells.
Narrow tubes called ureters carry urine from the kidneys to the
bladder, a triangle-shaped chamber in the lower abdomen. Like a
balloon, the bladder's elastic walls stretch and expand to store
urine. They flatten together when urine is emptied through the
urethra to outside the body.
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A kidney stone is a hard mass developed from crystals that
separate from the urine and build up on the inner surfaces of the
kidney. Normally, urine contains chemicals that prevent the crystals
from forming. These inhibitors do not seem to work for everyone,
however, so some people form stones. If the crystals remain tiny
enough, they will travel through the urinary tract and pass out of
the body in the urine without being noticed.
Kidney stones may contain various combinations of chemicals. The
most common type of stone contains calcium in combination with
either oxalate or phosphate. These chemicals are part of a person's
normal diet and make up important parts of the body, such as bones
A less common type of stone is caused by infection in the urinary
tract. This type of stone is called a struvite or infection stone. A
bit less common is the uric acid stone. Cystine stones are rare.
Kidney stones in kidney, ureter,
Urolithiasis is the medical term used to describe stones
occurring in the urinary tract. Other frequently used terms are
urinary tract stone disease and nephrolithiasis. Doctors also use
terms that describe the location of the stone in the urinary tract.
For example, a ureteral stone (or ureterolithiasis) is a kidney
stone found in the ureter. To keep things simple, however, the term
"kidney stones" is used throughout this fact sheet.
Gallstones and kidney stones are not related. They form in
different areas of the body. If you have a gallstone, you are not
necessarily more likely to develop kidney stones.
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For unknown reasons, the number of people in the United States
with kidney stones has been increasing over the past 20 years. White
Americans are more prone to develop kidney stones than African
Americans. Stones occur more frequently in men. Kidney stones strike
most typically between the ages of 20 and 40. Once a person gets
more than one stone, others are likely to develop.
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Doctors do not always know what causes a stone to form. While
certain foods may promote stone formation in people who are
susceptible, scientists do not believe that eating any specific food
causes stones to form in people who are not susceptible.
A person with a family history of kidney stones may be more
likely to develop stones. Urinary tract infections, kidney disorders
such as cystic kidney diseases, and metabolic disorders such as
hyperparathyroidism are also linked to stone formation.
In addition, more than 70 percent of people with a rare
hereditary disease called renal tubular acidosis develop kidney
Cystinuria and hyperoxaluria are two other rare, inherited
metabolic disorders that often cause kidney stones. In cystinuria,
too much of the amino acid cystine, which does not dissolve in
urine, is voided. This can lead to the formation of stones made of
cystine. In patients with hyperoxaluria, the body produces too much
of the salt oxalate. When there is more oxalate than can be
dissolved in the urine, the crystals settle out and form stones.
Shapes of various stones. Sizes
are usually smaller than shown here.|
Hypercalciuria is inherited. It is the cause of stones in more
than half of patients. Calcium is absorbed from food in excess and
is lost into the urine. This high level of calcium in the urine
causes crystals of calcium oxalate or calcium phosphate to form in
the kidneys or urinary tract.
Other causes of kidney stones are hyperuricosuria (a disorder of
uric acid metabolism), gout, excess intake of vitamin D, and
blockage of the urinary tract. Certain diuretics (water pills) or
calcium-based antacids may increase the risk of forming kidney
stones by increasing the amount of calcium in the urine.
Calcium oxalate stones may also form in people who have a chronic
inflammation of the bowel or who have had an intestinal bypass
operation, or ostomy surgery. As mentioned above, struvite stones
can form in people who have had a urinary tract infection. People
who take the protease inhibitor indinavir, a drug used to treat HIV
infection and AIDS, are at risk of developing kidney stones.
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Usually, the first symptom of a kidney stone is extreme pain. The
pain often begins suddenly when a stone moves in the urinary tract,
causing irritation or blockage. Typically, a person feels a sharp,
cramping pain in the back and side in the area of the kidney or in
the lower abdomen. Sometimes nausea and vomiting occur. Later, pain
may spread to the groin.
If the stone is too large to pass easily, 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 appear
in the urine. As the stone moves down the ureter closer to the
bladder, you may feel the need to urinate more often or feel a
burning sensation during urination.
If fever and chills accompany any of these symptoms, an infection
may be present. In this case, you should contact a doctor
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Sometimes "silent" stones--those that do not cause symptoms--are
found on x rays taken during a general health exam. These stones
would likely pass unnoticed.
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. These
diagnostic images give the doctor valuable information about the
stone's size and location. Blood and urine tests help detect any
abnormal substance that might promote stone formation.
The doctor may decide to scan the urinary system using a special
x ray test called an IVP (intravenous pyelogram). The results of all
these tests help determine the proper treatment.
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Fortunately, surgery is not usually necessary. Most kidney stones
can pass through the urinary system with plenty of water (2 to 3
quarts a day) to help move the stone along. Often, you can stay home
during this process, drinking fluids and taking pain medication as
needed. The doctor usually asks you to save the passed stone(s) for
testing. (You can catch it in a cup or tea strainer used only for
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If you've had more than one kidney stone, you are likely to form
another; so prevention is very important. To prevent stones from
forming, your doctor must determine their cause. He or she will
order laboratory tests, including urine and blood tests. Your doctor
will also ask about your medical history, occupation, and eating
habits. If a stone has been removed, or if you've passed a stone and
saved it, the laboratory should analyze it because its composition
helps in planning treatment.
You may be asked to collect your urine for 24 hours after a stone
has passed or been removed. The sample is used to measure urine
volume and levels of acidity, calcium, sodium, uric acid, oxalate,
citrate, and creatinine (a product of muscle metabolism). Your
doctor will use this information to determine the cause of the
stone. A second 24-hour urine collection may be needed to determine
whether the prescribed treatment is working.
A simple and most important lifestyle change to prevent stones is
to drink more liquids--water is best. If you tend to form stones,
you should try to drink enough liquids throughout the day to produce
at least 2 quarts of urine in every 24-hour period.
People who form calcium stones used to be told to avoid dairy
products and other foods with high calcium content. But recent
studies have shown that foods high in calcium, including dairy
foods, help prevent calcium stones. Taking calcium in pill form,
however, may increase the risk of developing stones.
You may be told to avoid food with added vitamin D and certain
types of antacids that have a calcium base. If you have very acidic
urine, you may need to eat less meat, fish, and poultry. These foods
increase the amount of acid in the urine.
To prevent cystine stones, you should drink enough water each day
to dilute the concentration of cystine that escapes into the urine,
which may be difficult. More than a gallon of water may be needed
every 24 hours, and a third of that must be drunk during the
Foods and Drinks Containing Oxalate
People prone to forming calcium oxalate stones may be asked
by their doctor to cut back on certain foods if their urine
contains an excess of oxalate:
- wheat bran
People should not give up or avoid eating these foods
without talking to their doctor first. In most cases, these
foods can be eaten in limited amounts.
The doctor may prescribe certain medications to prevent calcium
and uric acid stones. These drugs control the amount of acid or
alkali in the urine, key factors in crystal formation. The drug
allopurinol may also be useful in some cases of hyperuricosuria.
Doctors usually try to control hypercalciuria, and thus prevent
calcium stones, by prescribing certain diuretics, such as
hydrochlorothiazide. These drugs decrease the amount of calcium
released by the kidneys into the urine by favoring calcium retention
in bone. They work best when sodium intake is low.
Very rarely, patients with hypercalciuria may be given the drug
sodium cellulose phosphate, which binds calcium in the intestines
and prevents it from leaking into the urine.
If cystine stones cannot be controlled by drinking more fluids,
your doctor may prescribe drugs such as Thiola and Cuprimine, which
help reduce the amount of cystine in the urine.
For struvite stones that have been totally removed, the first
line of prevention is to keep the urine free of bacteria that can
cause infection. Your urine will be tested regularly to be sure that
no bacteria are present.
If struvite stones cannot be removed, your doctor may prescribe a
drug called acetohydroxamic acid (AHA). AHA is used with long-term
antibiotic drugs to prevent the infection that leads to stone
People with hyperparathyroidism sometimes develop calcium stones.
Treatment in these cases is usually surgery to remove the
parathyroid glands (located in the neck). In most cases, only one of
the glands is enlarged. Removing the glands cures the patient's
problem with hyperparathyroidism and with kidney stones as
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Surgery should be reserved as an option for cases where other
approaches have failed or should not be tried. Surgery may be needed
to remove a kidney stone if it
- does not pass after a reasonable period of time and causes
- is too large to pass on its own or is caught in a difficult
- blocks the flow of urine
- causes ongoing urinary tract infection
- damages kidney tissue or causes constant bleeding
- has grown larger (as seen on followup x ray studies).
Until recently, surgery to remove a stone was very painful and
required a recovery time of 4 to 6 weeks. Today, treatment for these
stones is greatly improved, and many options do not require major
Extracorporeal Shockwave Lithotripsy
Extracorporeal shockwave lithotripsy (ESWL) is the most
frequently used procedure for the treatment of kidney stones. In
ESWL, shock waves that are created outside the body travel through
the skin and body tissues until they hit the denser stones. The
stones break down into sand-like particles and are easily passed
through the urinary tract in the urine.
Extracorporeal shockwave lithotripsy|
There are several types of ESWL devices. In one device, the
patient reclines in a water bath while the shock waves are
transmitted. Other devices have a soft cushion on which the patient
lies. Most devices use either x rays or ultrasound to help the
surgeon pinpoint the stone during treatment. For most types of ESWL
procedures, anesthesia is needed.
In some cases, ESWL may be done on an outpatient basis. Recovery
time is short, and most people can resume normal activities in a few
Complications may occur with ESWL. Most patients have blood in
their urine for a few days after treatment. Bruising and minor
discomfort in the back or abdomen from the shock waves are also
common. To reduce the risk of complications, doctors usually tell
patients to avoid taking aspirin and other drugs that affect blood
clotting for several weeks before treatment.
Another complication may occur if the shattered stone particles
cause discomfort as they pass through the urinary tract. In some
cases, the doctor will insert a small tube called a stent through
the bladder into the ureter to help the fragments pass. Sometimes
the stone is not completely shattered with one treatment, and
additional treatments may be needed. ESWL is not ideal when stones
are larger than 2 centimeters, about 0.8 inches.
Sometimes a procedure called percutaneous nephrolithotomy is
recommended to remove a stone. This treatment is often used when the
stone is quite large or in a location that does not allow effective
use of ESWL.
In this procedure, the surgeon makes a tiny incision in the back
and creates a tunnel directly into the kidney. Using an instrument
called a nephroscope, the surgeon locates and removes the stone. For
large stones, some type of energy probe (ultrasonic or
electrohydraulic) may be needed to break the stone into small
pieces. Generally, patients stay in the hospital for several days
and may have a small tube called a nephrostomy tube left in the
kidney during the healing process.
One advantage of percutaneous nephrolithotomy over ESWL is that
the surgeon removes the stone fragments instead of relying on their
natural passage from the kidney.
Ureteroscopic Stone Removal
|Ureteroscopic stone removal
Although some kidney stones in the ureters can be treated with
ESWL, ureteroscopy may be needed for mid- and lower-ureter stones.
No incision is made in this procedure. Instead, the surgeon passes a
small fiberoptic instrument called a ureteroscope through the
urethra and bladder into the ureter. The surgeon then locates the
stone and either removes it with a cage-like device or shatters it
with a special instrument that produces a form of shock wave. A
small tube or stent may be left in the ureter for a few days to help
the lining of the ureter heal. Before fiber optics made ureteroscopy
possible, physicians used a similar "blind basket" extraction
method. But this outdated technique should not be used because it
may damage the ureters.
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The Division of Kidney, Urologic, and Hematologic Diseases of the
National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK) funds research on the causes, treatments, and prevention of
kidney stones. NIDDK is part of the Federal Government's National
Institutes of Health in Bethesda, Maryland.
New drugs and the growing field of lithotripsy have greatly
improved the treatment of kidney stones. Still, NIDDK researchers
and grantees seek to answer questions such as
- Why do some people continue to have painful stones?
- How can doctors predict, or screen, those at risk for getting
- What are the long-term effects of lithotripsy?
- Do genes play a role in stone formation?
- What is the natural substance(s) found in urine that blocks
Researchers are also working on new drugs with fewer side
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- If you have a family history of stones or have had more than one stone,
you are likely to develop more stones.
- A good first step to prevent the formation of any type of stone is to
drink plenty of liquids--water is best.
- If you are at risk for developing stones, your doctor may perform certain
blood and urine tests to determine which factors can best be altered to
reduce that risk.
- Some people will need medicines to prevent stones from forming.
- People with chronic urinary tract infections and stones will often need
the stone removed if the doctor determines that the infection results from
the stone's presence. Patients must receive careful followup to be sure
that the infection has cleared.
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American Foundation for Urologic Disease
National Kidney Foundation
Oxalosis and Hyperoxaluria Foundation (OHF)
National Institute of Diabetes and Digestive and Kidney
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