A kidney stone is a hard, pebble-like deposit that forms in one or both kidneys. It may travel down through the urinary tract. The stones may be as small as a grain of sand or as large as a pearl. Rarely, they can be as big as golf balls. A stone may be smooth, irregular in shape, or jagged. Most are yellow or brown in color. There are different types of kidney stones:

• Calcium stones. Calcium stones are the most common type of stones. Calcium is a normal part of healthy eating and is used by bones and muscles. Calcium not used by the body goes to the kidneys where it is normally flushed out with the urine. In some people, the calcium that stays behind bonds with other waste products to form a stone.
• Struvite stones. Struvite stones contain the mineral magnesium and the waste product ammonia. This type may form after an infection in the urinary tract.
• Uric acid stones. Uric acid stones may form when there is too much acid in the urine. This type can be seen in people who have gout.
• Cystine stones. Cystine is one of the building blocks that make up muscles, nerves, and other parts of the body. It can build up in the urine and form a stone. Cystine stones are rare and often run in families.

Kidney stones are very painful. They are also one of the most common problems of the urinary tract.

A kidney stone develops from crystals that build up in the kidney. Urine normally contains chemicals that prevent or slow the crystals from forming. But stones still form in some people. Small crystals can travel through the urinary tract and pass out of the body in the urine without even being noticed. A larger stone can get stuck in a ureter. The ureter is the small tube between the kidney and the bladder. A large stone can also get stuck in the bladder or the urethra. The urethra is the tube from the bladder that takes urine out of the body. A large stone may block the flow of urine and cause great pain.

You are more likely to get a kidney stone if you:

• Are white. White people are at higher risk than African Americans.
• Are biologically male. Kidney stones happen more often in biological males, but the number of biological females who get kidney stones has been growing.
• Are age 20 to 40.
• Have had a stone in the past. Once you've had one stone, you are more likely to get more.

These are factors you can control:

• How much fluid you drink. If you don't drink enough fluids and tend to be dehydrated, you are at a higher risk for kidney stones.
• Your diet. Eating a diet that is high in protein, sodium, and dark green vegetables (oxalate-rich types of foods) can increase your risk for kidney stones.
• Your weight. Being at a higher weight increases insulin resistance in your body. Insulin resistance increases the amount of calcium filtered into the urine. In turn, that increases the risk of developing a kidney stone.
• Medicines. Some medicines can increase your risk for kidney stones. Common medicines include water pills (diuretics) and antiviral medicines.

These are things you can't control:

• Certain diseases that cause ongoing higher levels of calcium in the blood. More calcium can cause dehydration because you make more urine. The extra calcium in the kidney solidifies into a stone.
• Surgery. Surgeries on the digestive tract, including the intestines and gastric bypass, can make you more likely to have long-term (chronic) dehydration. Or you may develop diseases that cause chronic diarrhea and dehydration. These increase the risk for kidney stones.
• Family history. Inherited factors or a family history of kidney stones can raise your risk.
• Past urinary tract infections that kept returning.
• Low estrogen. People with low estrogen levels after menopause or after removal of the ovaries are at greater risk for kidney stones.
• Sex. Biological males between the ages of 30 and 50 are the most likely to get kidney stones.
• High uric acid level. Diseases that raise uric acid levels (gout) raise your risk for stones.
• Diabetes. Insulin resistance from diabetes can cause an increase in the amount of calcium filtered into the urine. That raises the risk for a kidney stone.

Some of the most common symptoms of kidney stones include:

• Extreme, sharp pain in the back, side, lower belly (abdomen), or groin that will not go away. Changing positions doesn't help. Pain may last for a short or long time and may come and go in waves.
• Blood in the urine.
• Nausea and vomiting.
• Cloudy or odorous urine.
• Frequent urination.
• Not being able to urinate or urinating only a small amount.
• A burning feeling when you urinate.
• Fever and chills.

The symptoms of kidney stones may look like other health problems. Contact your doctor to get medical care right away.

Your doctor will ask about your health history and do a physical exam. You may have other tests. These include:

• CT scan. This imaging test uses X-rays and a computer to make detailed images of the body. A CT scan shows details of the bones, muscles, fat, and organs. This is the test of choice to find out if there is a kidney stone.
• Urinalysis. This lab exam looks at urine for various cells and chemicals, such as red blood cells, white blood cells, infection, or extra protein.
• Blood tests. These are lab exams of the blood to look for substances that might cause a stone to form. These tests can also assess how well your kidneys are working.
• Renal ultrasound. This noninvasive test bounces sound waves off the kidney. It sends a picture of the kidney to a video screen. This test is used to find the size and shape of the kidney. It can also see a mass, kidney stone, cyst, or other blockage in the kidney.
• Intravenous pyelogram (IVP). This test is a series of X-rays of the kidneys, ureters, and bladder, using an injection of contrast dye into the vein. It helps find tumors, kidney stones, or blockages. It can also check blood flow to the kidneys. This test is sometimes done if a CT scan and ultrasound can't be done.

Treatment will depend on your symptoms, age, and general health. It will also depend on how severe the condition is.

See your doctor right away if you think you have a kidney stone. Some kidney stones pass out of the body on their own without treatment. In cases that cause lasting symptoms or other complications, kidney stones may be treated with one of the following:

• Shock waves or extracorporeal shock wave lithotripsy (ESWL). This treatment uses a machine to send shock waves directly to the kidney stone. It breaks a large stone into smaller stones that will pass through the urinary tract. There are two types of shock wave machines. In one, you sit in a tub of water. In the other, you lie on a table.
• Ureteroscope. A long wire with a camera attached to it is inserted into the urethra. The wire is passed up through the bladder to the ureter where the stone is located. A tiny cage is used to grab the stone and remove it.
• Tunnel surgery (percutaneous nephrolithotomy). A small cut is made in your back and a narrow tunnel is made through the skin to the stone inside the kidney. The surgeon can remove the stone through this tunnel.
• Potassium citrate. Your doctor may prescribe potassium citrate tablets to treat stones made of calcium and uric acid that aren't causing a blockage. You take the tablets with plenty of fluids. The citrate may help dissolve and drain the stone with the additional fluid.

The best ways to prevent kidney stones are to:

• Drink more water to prevent dehydration. Up to 12 glasses of water a day, or as your doctor advises, can help to flush away the substances that form stones in the kidneys. Ginger ale, lemon-lime sodas, and fruit juices are also okay. But water is preferred.
• Limit coffee, tea, and cola to 1 or 2 cups a day. The caffeine may cause a rapid loss of fluid.
• Talk with your doctor or a dietitian about any diet changes.
• Take medicines prescribed to prevent calcium and uric acid stones from forming.

Contact your doctor or seek immediate medical attention if your symptoms get worse or you have new symptoms.

• A kidney stone is a piece of hard sediment that forms in the kidney. It develops when certain substances that are filtered in the urine crystallize, stick together in the kidney, and create a stone.
• Most stones are made of calcium, although stones can be formed from other substances.
• Dehydration and certain medicines also increase the risk for kidney stones.
• Kidney stones cause pain with urination as the stone passes through the urinary tract.
• Some kidney stones can't be passed out of your body because they are too large and become stuck in the urinary tract. This causes great pain. It may also block the flow of urine. This needs medical care right away.
• You may be able to prevent kidney stones by staying away from certain foods and drinking plenty of water.
• Once you have had a kidney stone, you are more likely to have another stone.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions.