Kidney stones are
stones formed from chemicals in urine that
crystallize and stick together. Some cause problems,
and others we may never know they're there.
If you've ever passed a kidney stone, you're not
likely to forget the experience - it can be
excruciatingly painful. What's more, kidney stones
(renal lithiasis) are increasingly common.
Not all kidney stones cause symptoms. They're
often discovered when you have X-rays for an
unrelated condition or when you seek medical care
for problems such as blood in your urine or
recurring urinary tract infections. The pain becomes
agonizing only when a stone breaks loose and begins
to work its way down from your kidneys to your
Kidney stones usually form when your urine
becomes too concentrated. This causes minerals and
other substances in urine to form crystals on the
inner surfaces of your kidneys. Over time, these
crystals may combine to form a small, hard mass, or
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.
Most small kidney stones pass into your bladder
without causing any permanent damage. Still, it's
important to determine the underlying cause so that
you don't form more stones in the future. In many
cases, you can prevent kidney stones simply by
drinking more water and making a few dietary
Signs and symptoms
You're not likely to have signs and symptoms unless a kidney stone is
large, causes a blockage, is associated with an infection or is being
passed. Then the most common symptom is an intense, colicky pain that
may fluctuate in intensity over periods of 5 to 15 minutes. The pain
usually starts in your back or your side just below the edge of your
ribs. As the stone moves down the ureter toward your bladder, the pain
may radiate to your groin. If the stone stops moving, the pain may stop
too. Other signs and symptoms may include:
Bloody, cloudy or
Persistent urge to
Fever and chills
if an infection is present
Your kidneys are two bean-shaped organs, each about the size of your
fist. They're located in back of your abdomen on either side of your
spine, and their main function is to remove excess fluid and waste from
your blood in the form of urine. The ureters carry urine from your
kidneys to your bladder, where it's stored until you eliminate it from
The crystals that lead to kidney stones are likely to form when your
urine contains a high concentration of certain substances — especially
calcium, oxalate, uric acid and cystine — or low levels of substances
that help prevent crystal formation, such as citrate and magnesium.
Crystals also may form if your urine becomes too concentrated or is too
acidic or too alkaline.
number of factors can cause changes in your urine, including the effects
of heredity, diet, drugs, climate, lifestyle factors and certain medical
conditions. Each of the four main types of kidney stones has a different
Approximately 75 percent to 85 percent of all kidney stones are
calcium stones. These stones are usually a combination of calcium
and oxalate, a compound that occurs naturally in some fruits and
vegetables. A number of factors can cause high concentrations of
these substances in urine. Excess calcium, for instance, may result
from ingesting large amounts of vitamin D, from treatment with
thyroid hormones or certain diuretics, and from some cancers and
kidney conditions. You may also have high levels of calcium if your
parathyroid glands, which regulate calcium metabolism, are
overactive (hyperparathyroidism). On the other hand, certain genetic
factors, intestinal bypass surgery and a diet high in oxalic acid
may cause excess amounts of oxalate in your body.
These stones are formed of uric acid, a byproduct of protein
metabolism. You're more likely to develop uric acid stones if you've
undergone chemotherapy, you eat a high-protein diet or you have
certain genetic factors that predispose you to the condition.
Found more often in women than in men, struvite stones are almost
always the result of chronic urinary tract infections caused by
bacteria that produce specific enzymes. These enzymes increase the
amount of ammonia in the urine, which is incorporated in the
crystals of struvite stones. These stones are often large and have a
characteristic stag's horn shape that can seriously damage your
These stones represent only about 1 percent of kidney stones. They
form in people with a hereditary disorder that causes the kidneys to
excrete excessive amounts of certain amino acids (cystinuria).
These factors may increase your risk of developing kidney stones:
Lack of fluids.
If you don't drink enough fluids, especially water, your urine is
likely to have higher concentrations of substances that can form
stones. That's also why you're more likely to form kidney stones if
you live in a hot, dry climate, work in a hot environment such as a
commercial kitchen or exercise strenuously without replacing lost
or personal history.
If someone in your family has kidney stones, you're more likely to
develop stones too. And if you've already had one or more kidney
stones, you're at increased risk of developing another.
Age, sex and
Most people who develop kidney stones are between 20 and 40 years of
age. Men are more likely to develop kidney stones than women are,
although for unknown reasons the number of women with kidney stones
is increasing. In addition, white Americans are at higher risk of
kidney stones than are black Americans.
Rare, inherited diseases such as renal tubular acidosis and
cystinuria can increase your risk of kidney stones. So can more
common disorders such as gout, chronic urinary tract infections,
cystic kidney disease and hyperparathyroidism.
Medications can have variable effects on stone formation. For
example, diuretics may increase your risk of developing kidney
stones in some situations and decrease it in others. If you're at
risk, check with your doctor or pharmacist about any medications you
A diet that's high in protein (meat, chicken and fish) and low in
fiber (fruits, vegetables and whole grains) may increase your risk
of some types of kidney stones.
You're more prone to develop kidney stones if you're bedridden or
very sedentary for a period of time. That's because limited activity
can cause your bones to release more calcium.