What are kidney stones?
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, we use the term "kidney stones" on this Web site.
Kidney stones are one of the most painful disorders to afflict humans
and are also one of the most common disorders of the urinary tract.
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.
Who is at risk for kidney stones?
It is estimated that 10 percent of all people in the United States will
have kidney stones at some point in their lives. Men tend to be affected
more frequently than women. For some unknown reason, the number of
persons in the United States with kidney stones has been increasing over
the past 20 years. Caucasians are more prone to kidney stones than
people of African-American descent. Although stones occur more
frequently in men, the number of women who get kidney stones has been
increasing over the past 10 years. 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.
What causes kidney stones?
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.
We do not always know what causes stones 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.
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. Struvite stones can form in people who have had a
urinary tract infection.
A person with a family history of kidney stones may be more likely to
develop stones. Urinary tract infections, kidney disorders (e.g., cystic
kidney diseases) and metabolic disorders (e.g., hyperparathyroidism) are
also linked to stone formation. In addition, more than 70 percent of
patients with the hereditary disease renal tubular acidosis develop
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.
What are the symptoms?
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
of 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, our office should
be contacted immediately.
How are kidney stones diagnosed?
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 us valuable information about the stone's size
and location. Blood and urine tests help detect any abnormal substance
that might promote stone formation. 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.
How are kidney stones treated?
Fortunately, most stones can be treated without surgery. Most kidney
stones can pass through the urinary system when the person drinks plenty
of water (two to three 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. You are usually asked to save the passed stone(s)
for testing. For surgical alternatives, see our kidney stone prevention
and treatment FAQ.