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Health Information
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Sunday, May 18, 2008
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Kidney
Stones In Adults
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What Are
Kidney Stones?
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Overview
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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.
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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 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 document.
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.
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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.
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Dctors 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.
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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 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
during urination.
If fever and
chills accompany any of these symptoms, an infection may
be present. In this case, a doctor should be contacted
immediately.
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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). Together,
the results from these tests help determine the proper
treatment.
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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.
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 24-hour period.
Patients with
too much calcium or oxalate in the urine may need to eat
fewer foods containing calcium and oxalate.
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
hyperuricosuria.
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 growth.
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 stone:
- does not
pass after a reasonable period of time and causes constant
pain,
- 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 major surgery.
Extracorporeal
Shockwave Lithotripsy. Extracorporeal shockwave
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 urine.
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 days.
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.
ercutaneous
Nephrolithotomy. 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 EWSL.
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.
Ureteroscopic
Stone Removal. Although some 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.
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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
stones?
- 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 formation?
Researchers are
also working to develop new drugs with fewer side effects.
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- 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 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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Persons
prone to forming calcium oxalate stones may be asked by
their doctor to cut back on certain foods on this list.
- apples
- asparagus
- beer
- beets
- berries,
various (e.g., cranberries, strawberries)
- black pepper
- broccoli
- cheese
- chocolate
- cocoa
- coffee
- cola drinks
- collards
- figs
- grapes
- ice cream
- milk
- oranges
- parsley
- peanut butter
- pineapples
- spinach
- Swiss chard
- rhubarb
- tea
- turnips
- vitamin
C
- yogurt
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 limited amounts.
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Understanding
Kidney Stones . . . Management for a Lifetime,
Krames Communication, 110 Grundy Lane, San Bruno, CA 94066.
(800) 333-3032.
Coe, F.L.,
et al., The Pathogenesis and Treatment of Kidney Stones,
New England Journal of Medicine, Vol. 327, No.
16, pp.1141-1152, 1992.
Curhan, G.C.,etal.,
A Prospective Study of Dietary Calcium and Other Nutrients
and the Risk of Symptomatic Kidney Stones, New England
Journal of Medicine, Vol. 328, No. 12, pp. 833-838,
1993.
Jenkins, A.D.,
Upgrading Extracorporeal Shock Wave Lithotripsy, Contemporary
Urology, October 1991, pp. 11-12.
Lawson, R.K.,
Smaller Means Safer Intraureternal Eletrohydraulic Lithotripsy,
Comtemporary Urology, October 1991, pp.51-58.
Lingeman,J.E.,
et al., Kidney Stones: Acute Management, Patient Care,
August 15, 1990, pp.20-42.
Lingeman, J.E.,
et al., Kidney Stones: Identifying the Causes, Patient
Care, September 30, 1990, pp.31-46.
O'Brien, W.M.,
Rotolo, J.E., Pahira, J.J., New Approaches in the Treatment
of Renal Calculi, American Family Physician, November
1987, pp. 181-94.
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American
Foundation for Urologic Disease
300 West Pratt Street
Baltimore, MD 21201-2463
(800) 242-2383; (410) 727-2908
National Kidney
Foundation
30 East 33rd Street
New York, NY 10016
(800) 622-9010; (212) 889-2210
National Kidney
and Urologic Diseases Information Clearinghouse
3 Information Way
Bethesda, MD 20892-3580
Oxalosis and
Hyperoxaluria Foundation
12 Pleasant Street
Maynard, MA 01754
(888) 712-2432 PIN# 5392; (508) 461-0614
For information
about hyperparathyroidism:
National Institute of Diabetes and Digestive and Kidney
Diseases
Building 31, Room 9A04
9000 Rockville Pike
Bethesda, MD 20892
(301) 496-3583
For information
about gout:
National Arthritis and Musculoskeletal and Skin Diseases
Information Clearinghouse
Box AMS
9000 Rockville Pike
Bethesda, MD 20892
(301) 495-4484
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National Kidney
and Urologic Diseases Information Clearinghouse
3
Information Way
Bethesda, MD 20892-3580
E-mail: nkudic@info.niddk.nih.gov
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NIH Publication No. 94-2495
April 1994
e-text posted: 12 February 1998
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