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Kidney stones are one of the most painful disorders to afflict humans.
This ancient health problem has tormented people throughout history.
Scientists have even found evidence of kidney stones in an Egyptian
mummy estimated to be more than 7,000 years old.
Kidney stones are one of the most common disorders of the urinary
tract. More than 1 million cases of kidney stones were diagnosed in
1985. It is estimated that 10 percent of all people in the United States
will have a kidney stone at some point in time. Men tend to be affected
more frequently than women.
Most kidney stones pass out of the body without any intervention by a
physician. Cases that cause lasting symptoms or other complications
may be treated by various techniques, most of which do not involve
major surgery. Research advances also have led to a better
understanding of the many factors that promote stone formation.
An Introduction to 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.
What Is a
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.
These inhibitors do not seem to
work for everyone, however, and
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 even 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 and muscles.
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. Much less
common are the uric acid stone and the rare cystine stone.
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, the term "kidney stones" is used throughout this e-text
Gallstones and kidney stones are not related. They form in different
areas of the body. If a person has a gallstone, he or she is not
necessarily more likely to develop kidney stones.
For some unknown reason, the number of persons in the United States
with kidney stones has been increasing over the past 20 years. White
people are more prone to kidney stones than are black people.
Although stones occur more frequently in men, the number of women
who get kidney stones has been increasing over the past 10 years,
causing the ratio to change. 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.
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 patients with adequate hereditary
disease called renal tubular acidosis develop kidney stones.
Cystinuria and hyuperoxaluria are two other rare inherited metabolic
disorders that often cause kidney stones. In cystinuria, the kidneys
produce too much of the amino acid cystine. Cystine does not dissolve
in urine and can build up to form stones. 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.
Absorptive hypercalciuria occurs when the body absorbs too much
calcium from food and empties the extra calcium 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 tact. 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.
What Are the
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
the back and side in the area of the kidney or in the lower abdomen.
Sometimes nausea and vomiting occur with this pain. Later, the pain
may spread to the groin.
If 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
If fever and chills accompany any of these symptoms, an infection may
be present. In this case, a doctor should be contacted immediately.
How Are Kidney
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). Together, the results from
these tests help determine the proper treatment.
How Are Kidney
Fortunately, most stones can be treated without surgery. 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. In most cases, a person can
stay home during this process, taking pain medicine as needed. The
doctor usually asks the patient to save the passed stone(s) for testing.
The First Step: Prevention
People who have had more than one kidney stone are likely to form
another. Therefore, prevention is very important. To prevent stones
from forming, their cause must be determined. The urologist will order
laboratory tests, including urine and blood tests. He or she will also ask
about the patient's medical history, occupation and dietary habits. If a
stone has been removed, or if the patient has passed a stone and saved
it, the lab can analyze the stone to determine its composition.
A patient may be asked to collect his or her 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 byproduct of protein metabolism). The doctor
will use this information to determine the cause of the stone. A second
24-hour urine collection may be needed to determine if the prescribed
treatment is working.
Lifestyle Changes. A simple
and most important lifestyle
change to prevent stones is to
drink more liquids--water is best.
A recurrent stone former should
try to drink enough liquids
throughout the day to produce at
least 2 quarts of urine in every
Patients with too much calcium or
oxalate in the urine may need to eat fewer foods containing calcium and
Not everyone will benefit from a low-calcium diet, however. Some
patients who have high levels of oxalate in their urine may benefit from
extra calcium in their diet. patients may be told to avoid food with
added vitamin D and certain types of antacids that have a calcium base.
Patients who have a very acid urine may need to eat less meat, fish, and
poultry. These foods increase the amount of acid in the urine.
To prevent cystine stones, patients should drink enough water each day
to reduce the amount of cystine that escapes into the urine. This is
difficult because more than a gallon of water may be needed every 24
hours, a third of which must be drunk during the night.
Medical Therapy. 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 hypercalciuria and
Another way a doctor may try to control hypercalciuria, and thus
prevent calcium stones, is by prescribing certain diuretics, such as
hydrochlorothiazide. These drugs decrease the amount of calcium
released by the kidneys into the urine.
Some patients with absorptive hypercalciuria may be given the drug
sodium cellulose phosphate. This drug binds calcium in the intestine and
prevents it from leaking into the urine.
If cystine stones cannot be controlled by drinking more fluids, the
doctor may prescribe the drug Thiola. This medication helps 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.
The patient's urine will be tested on a regular basis to be sure that
bacteria are not present.
If struvite stones cannot be removed the doctor may prescribe a new
drug called aetohydroamic acid (AHA). AHA is used along with
long-term antibiotic drugs to prevent the infection that leads to stone
To prevent calcium stones that form in hyperparathyroid patients, a
surgeon may remove all of the parathyroid glands (located in the neck).
This is usually the treatment for hyperparathyroidism as well. In most
cases, only one of the glands is enlarged. Removing the gland ends the
patient's problem with kidney stones.
Some type of surgery may be needed to remove a kidney stone if the
- does not pass after a reasonable period of time and causes
- is too large to pass on its own
- blocks the urine flow
- causes ongoing urinary tract infection
- damages the kidney tissue or causes constant bleeding, or
- has grown larger (as seen on follow up x-ray studies).
Until recently, surgery to remove a stone was very painful and required
a lengthy recovery time (4 to 6 weeks). Today, treatment for these
stones is greatly improved. Many options exist that do not require
lithotripsy (ESWL) is the
most frequently used
surgical procedure for the
treatment of kidney stones.
ESWL uses shockwaves
that are created outside of
the body to travel through
the skin and body tissues
until the waves hit the
dense stones. The stones
become sand-like and are easily passed through the urinary tract in the
There are several types of ESWL devices. One device positions the
patient in the water bath while the shock waves are transmitted. Other
devices have a soft cushion or membrane 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, some type of 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 the
urine for a few days after treatment. Bruising and minor discomfort on
the back or abdomen due to the shockwaves are also common. To
reduce the chances of complications, doctors usually tell patients to
avoid taking aspirin and other drugs that affect blood clotting for several
weeks before treatment.
In addition, the shattered stone fragments may cause discomfort as they
pass through the urinary tract in the urine. 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 required.
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
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 stone is
located and removed. 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 nephrokithotomy over ESWL is that
the surgeon removes the stone fragments instead of relying on their
natural passage from the kidney.
ureteral stones can be treated
with ESWL, urethroscopy 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 shockwave. A small tube or
stent may be left in the ureter for a few days after treatment to help the
lining of the ureter heal.
Is There Any
The Division of Kidney, Urologic, and Hematologic Diseases of the
National Institutes of Diabetes and Digestive and Kidney Diseases
(NIDDK) funds research on the causes, treatments, and prevention of
kidney stones. The 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, who is as 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 stone
Researchers are also working to develop new drugs with fewer side
People who have a family history of stones or who have had
more than one stone are likely to develop another.
A good first step to prevent any type of stone is to drink plenty
of liquids--water is best.
If a person is at risk for developing stones, the doctor may
perform certain blood and urine tests. These tests will determine
which factors can be best altered to reduce that risk.
Some patients will need medicines to prevent stones from
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.
Foods and Drinks Containing Caalcium and Oxalate
Persons prone to forming calcium oxalate stones may be asked by their
doctor to cut back on certain foods on this list.
(e.g., cranberries, strawberries)
Persons should not give up or avoid eating these types of foods without
talking to their doctor first. In most cases, these foods can be eaten in
The National Kidney and Urologic Diseases Information Clearinghouse
(NKUDIC) is a service of the National Institute of Diabetes and
Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the
National Institutes of Health under the U.S. Public Health Service.
Established in 1987, the clearinghouse provides information about
diseases of the kidneys and urologic system to people with kidney and
urologic disorders and to their families, health care professionals, and
the public. NKUDIC answers inquiries; develops, reviews, and
distributes publications; and works closely with professional and patient
organizations and Government agencies to coordinate resources about
kidney and urologic diseases.
Publications produced by the clearinghouse are carefully reviewed for
scientific accuracy, content, and readability.
Information provided by NIH.