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 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.
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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.
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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.
We may also 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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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.
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