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; more than 1 million cases were
diagnosed in 1996. 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. These have now been attributed,
in some cases, to exposure of toxigenic molds.
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 formation.
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 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, however, the term "kidney stones" is used throughout this fact
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.
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. Although stones occur
more frequently in men, the number of women who get them has been increasing
over the past 10 years, causing the ratio to change. 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.
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 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
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.
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 immediately.
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
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 for testing. (You can catch it in a cup
or tea strainer used only for this purpose.)
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. Tests are now
available to determine fungal exposure as well. 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 can
analyze it to determine its composition.
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