What is a kidney stone?

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 a healthy diet 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. It 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.

What causes a kidney stone?

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.

Who is at risk for kidney stones?

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

• Are white. Whites are at higher risk than African Americans.
• Were assigned male at birth. Kidney stones happen more often in people assigned male at birth, but the number of people assigned female at birth who get kidney stones has been growing.
• Are ages 20 to 40
• Have had a stone in the past. Once you’ve had 1 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 overweight 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 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.
• Gender. People assigned male at birth 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.

What are the symptoms of kidney stones?

These are the most common symptoms of kidney stones:

• 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
• Can't urinate or you urinate only a small amount
• A burning feeling when you urinate
• Fever and chills

The symptoms of kidney stones may look like other health problems. Call your healthcare provider to get medical care right away.

How are kidney stones diagnosed?

Your healthcare provider 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 kidney, ureters, and bladder with the injection of a contrast dye into the vein. It helps find tumors, kidney stones, or blockages. It can also check blood flow to the kidney. This test is sometimes done if CT scan and ultrasound can't be done.

How are kidney stones treated?

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

See your healthcare provider 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 2 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 healthcare provider 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.

Can kidney stones be prevented?

The best ways to prevent kidney stones are:

• Drink more water to prevent dehydration. Up to 12 glasses of water a day, or as your healthcare provider advises, can help to flush away the substances that form stones in the kidneys. Ginger ale, lemon-lime sodas, and fruit juices are also OK. 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 healthcare provider or a dietitian about any diet changes.
• Take medicines prescribed to prevent calcium and uric acid stones from forming.

When should I call my healthcare provider?

Call your healthcare provider or seek immediate medical attention if your symptoms get worse or you have new symptoms.

Key points about kidney stones

• 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.

Next steps

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

• 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 provider 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 provider 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 provider if you have questions.

Identifying Kidney Stones

There are four general types of kidney stones. Your kidney stone’s size and shape determine whether it's likely to pass by itself. Knowing what a stone is made of (its composition) helps your healthcare provider find its cause and prescribe the best treatment. X-rays or scans can help show the stone's size and shape. Your healthcare provider may also give you a strainer to catch the stone while passing urine. The stone can then be sent to a lab for analysis. You may need other types of urine and blood tests to help identify the stone. These tests can also help identify causes for different types of stones. 

The tests can show:

• Size. A stone may be as small as a grain of sand. Some may be the size of a pebble. A few may be as large as a golf ball. Small stones may pass out of your body when you urinate.
• Shape. Small, smooth, round stones may pass easily. Jagged-edged stones often lodge inside the kidney or ureter. Staghorn stones can fill the entire renal pelvis and calyces.
• Composition. Most stones are made of calcium oxalate, a hard compound. Stones made of cystine or uric acid, or caused by infection (struvite stones), are less dense. Stones often contain more than one chemical.

Treating your stones

You and your healthcare provider will work together to form a treatment plan. Your provider may suggest that you let your stone pass naturally. Or you may choose to manage it with medicines. Certain procedures may also help, such as shock wave lithotripsy or using a camera inside the body to remove the stone (ureteroscopy). Once they find out the cause of the stone, you will be told how you can help prevent kidney stones in the future.