All About Kidney Stones
A kidney stone (nephrolithiasis) is a solid piece of material made from chemicals
that form in the kidney. It's made from substances that normally dissolve in the urine.
Each year more than half a million people go to the emergency room with kidney stone
Kidney stones often occur between age 20 and 70 and are more common in men than women.
If you get kidney stones, you may be more likely to get them in the future.
How stones form
Your urinary tract is made up of several parts:
Kidneys. These are 2 bean-shaped organs about the size of your fist.
Ureters. These are 2 narrow muscular tubes that drain urine from the kidneys into the bladder.
Bladder. This organ temporarily stores urine.
Urethra. This is the tube that empties urine from the bladder.
The kidneys make urine by removing extra water and waste from your blood. They also
help your body balance certain chemicals in your blood.
Kidney stones are made up of chemicals in your urine. These include:
Uric acid (urate)
Stones begin as crystals that build up inside the kidney. Small crystals can pass
from your body through the urine without you ever knowing about them. When the crystals
grow larger and become stones, they can get stuck in the ureter and block the flow
of urine. This causes infection and pain.
About 3 in 4 kidney stones contain calcium plus either oxalate or phosphate. A less
common type of stone is composed of struvite. It's caused by urinary tract infections.
It's made of magnesium ammonium phosphate. Struvite stones make up 1 to 1.5 in 10
kidney stones. About 1 in 10 of the remaining stones are made of uric acid. Uric acid
is made from purine. This is a nitrogen compound found in protein and made in your
liver. Fewer than 3 in 100 stones are made of the amino acid cystine. This type is
rare and tends to run in families.
Stones can be as small as a grain of sand or as large as a golf ball.
Salts in the urine
It's not always completely clear what causes kidney stones to form. Some people are
more likely to get them because of their family history of stones. In many cases,
they are caused by having too many salts in your urine. These salts are calcium oxalate,
uric acid, and cystine. Salts can build up in the kidney when you don’t have enough
urine or you have higher levels of the salts than normal. When the salts build up
to a certain point, they no longer dissolve. They form crystals instead. Normally,
the urine contains chemicals and enzymes that keep crystals from forming, or from
sticking to the inner surface of the kidney.
Certain conditions make it more likely that you will get kidney stones. Those conditions
In other words, changes in the way your body uses food and beverages may increase
your chances of growing crystals and getting kidney stones. Some types of kidney stones
run in families (hereditary).
Some rare disorders can cause kidney stones. Some of those disorders are:
Renal tubular acidosis. This is sometimes an inherited disease.
Cystinuria. This means that crystals of cystine form.
Hyperoxaluria. This means that crystals of oxalate form.
Absorptive hypercalciuria. This means that your body takes in too much calcium from
Chronic dehydration. This occurs from not drinking enough water.
Kidney stones are more common in people with high blood pressure. They are also more
common in people who have a disorder of uric acid metabolism (hyperuricosuria). Stones
are also common in people who:
Take in too much vitamin D
Have a blockage or infection of the urinary tract
Take certain water pills (diuretics) or calcium-based antacids
Have inflammatory bowel disease such as Crohn's disease or ulcerative colitis
Have had an intestinal bypass or ostomy surgery
Making a diagnosis
There are no true "warning signs" for kidney stones. Small stones are usually passed
unnoticed. Large stones often remain undetected until they become lodged in the ureter
and you have severe and sudden pain in the back or lower abdomen. The pain is usually
described as a sharp and cramping pain in the back, the side, or the lower belly (abdomen).
The pain may spread to the groin. There may also be blood in the urine, nausea, and
vomiting. If the stone is too large to pass, the muscles of the ureter tighten trying
to squeeze the stone into the bladder. Fever or chills usually mean there is an infection.
Sometimes stones stay in the kidneys and grow larger.
Most kidney stones can be diagnosed by an X-ray or ultrasound. These images tell your
healthcare provider the stone's size and location. Blood and urine tests help find
any abnormal substance that might help stones form. Some imaging tests can see if
fluid is backing up in the kidneys that could cause damage.
Your healthcare provider may decide to scan the urinary system using a CT scan or
a special X-ray test called an intravenous pyelogram (IVP). The results of these tests
and the others above help your healthcare provider figure out the diagnosis and the
right treatment for you.
Getting the stone out
In most cases, treatment means letting the stone pass naturally. Your healthcare provider
may give you medicine for pain relief. Then he or she will add fluids until the ureter
builds up enough pressure to push the stone out. You will usually be asked to catch
the stone in a strainer so it can be looked at in the lab. If the stone hasn't passed
in 8 to 12 hours, you may need to see a urologist for more treatments.
For stones that don't pass on their own, other treatments are used:
Extracorporeal shock wave lithotripsy (ESWL). This treatment uses an ultrasound machine to send shock waves through the skin and
body tissue toward the stone. The shock waves break the stone into small pieces that
can pass from your body in the urine.
Percutaneous nephrolithotomy. This is surger to remove stones that are too large or that can't be reached with
ESWL. A surgeon makes a small incision in your back and makes a tunnel to the kidney.
The stone is then taken out through a nephroscope. If the stone is very large, the
surgeon can put an energy probe in to break the stone into smaller pieces and then
remove the pieces. If you have this surgery, you will need to stay in the hospital
for 2 to 3 days.
Ureteroscopic stone removal. The surgeon puts a fiber optic tool into the urethra and the bladder. They then move
it into the ureter. After the stone is found, the surgeon removes it with a cage-like
basket device or shatters it with laser beams or shock waves. Often, the surgeon puts
a stent in the ureter to keep the tube widened and ease passing of the stone pieces.
Preventing kidney stones is important, especially if you've had a kidney stone in
the past. This is because you may be at a higher risk to form another. The National
Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says the preventive
treatment your healthcare provider gives you will depend on the type of stone you
have. For example, a medicine that helps prevent calcium stones will not work if you
have a struvite stone. The diet changes that help prevent uric acid stones may have
no effect on calcium stones. So careful study of the stone will help guide your treatment.
If you are overweight, losing weight may help.
The most important part of prevention is getting plenty of fluids. This dilutes your
urine and increases urination. More trips to the bathroom help remove extra chemicals
from the urine and kidneys. This lowers the chances of stone formation.
The NIDDK recommends that you drink at least 6 to 8 8-ounce glasses of fluid every
day, unless your provider tells you otherwise. Their drink of choice? Water. Water
is available to everyone and is inexpensive.
People who form kidney stones were once told to stay away from dairy products and
other foods that contained a lot of calcium. Recent studies have shown that foods
high in calcium actually help prevent stones, according to the NIDDK. But calcium
supplements may increase the risk of developing stones. It's important to talk with
your provider before taking calcium supplements.
Eat less protein
For some people, eating less protein, especially protein from meat, may help prevent
certain stones. Protein can increase uric acid, calcium, and oxalates in the urine.
Protein also reduces citrate.
If you are at risk for uric acid stones, you may be helped by eating fewer foods that
contain purines. These foods include sardines, yeast, and organ meats.
If you are a person who absorbs a lot of oxalate, you should not drink large amounts
of tea, because it has a lot of oxalate. You should also drink less or no alcohol.
Other foods to pass up include chocolate, beets, coffee, cola, nuts, rhubarb, spinach,
strawberries, and wheat bran.
Your healthcare provider may prescribe medicine to help prevent kidney stones. The
medicines control the amount of substances in the urine that form crystals or prevent
the infections that can lead to stone growth.
You should also limit how much salt (sodium) you get each day. Salt is another chemical
that must leave the body through the urine. The more chemicals that are in the urine,
the more likely you are to form a stone.
Are you at risk?
Things that may increase your chance of developing kidney stones are:
A family history of kidney stone formation
An inherited condition that causes the body to absorb too much calcium
A low level of citrate in the urine. This may help calcium stones form.
Overactive parathyroid glands
Urinary tract infections
High blood pressure