Kidney Stones

What Are Kidney Stones?

Kidney stones are solid, stone-like lumps that form within the kidneys. They can be as small as a grain of sand or as large as the size of a golf ball (sometimes even larger). Most stones are less than a third of an inch in diameter.

The stones are actually accumulations of mineral salts and other substances. Similar stones also can form in most other portions of theurinary tract.

Many of these stones are small enough to pass out of the body during urination, but some larger stones may partially or fully block the normal flow of urine. Kidney stones can cause intense pain and other symptoms.

About 10 percent of people will experience a kidney stone at some time during life. Kidney stones are a common cause of blockage of the urinary tract in adults, accounting for 1 of every 1,000 hospitalizations.

What Are Kidney Stones Made Of?

Kidney stones consist of:

  • A center that consists of crystal-like substances
  • A surrounding region that is composed of layers

Kidney stones are composed of different chemical substances. Each of the major types is named for its main chemical ingredient. They are:

Calcium Stones

Calcium stones are the most common type of kidney stones, accounting for 75 to 85 percent of all stones.

  • Most of these stones consist of calcium oxalate, or a combination of calcium oxalate and phosphate.
  • Their formation is linked to high levels of urinary calcium, or a combination of calcium and uric acid, in the urine.

Uric Acid Stones

Uric acid stones are relatively uncommon, accounting for 5 to 8 percent of all stones.

  • A high level of uric acid in the blood and urine can cause this type of stone.
  • They can form if a person’s urine becomes concentrated with certain dissolved substances that may make it more acidic.

Cystine Stones

Cystine stones are rare, accounting for less than one percent of all kidney stones.

  • These stones result from an inherited condition that causes an increase in the amount of cystine (an amino acid) in the urine.
  • Because cystine cannot dissolve easily in water, it cannot be reabsorbed from the urine into the blood. This increases the chances that a stone will form.

Struvite Stones

Struvite stones make up 10 to 15 percent of all kidney stones. Because these stones can be quite large, they can cause serious symptoms.

  • Struvite stones are formed because of infection by specific bacteria, which throws off the balance of acid in the urine.
  • These stones are mainly composed of ammonium and magnesium phosphate and resemble hard crystals.

Faces About Kidney Stones

  • Problems from kidney stones are fairly common, accounting for 1 of every 1,000 hospitalizations.
  • About 5 percent of all people have kidney stones.
  • There are four types of kidney stones: calcium stones, uric acid stones, cystine stones, and struvite stones.
  • Most of the time, there’s no way to tell why the most common type of stones – calcium stones – have formed, although experts believe water intake and diet may play a role.
  • Kidney stones are most commonly found among people in the United States and in other technologically developed countries, while bladder stones are more common among people in developing countries.
  • Excruciating pain is the main symptom of a kidney stone. But not all kidney stones cause symptoms.
  • The presence of a urinary tract infection can increase the severity of stone disease and make treatment more difficult.

What Is The Urinary System?

The urinary organ system consists of the following organs, located within the abdomen:


The role of the kidneys is to cleanse the blood and balance its fluids:

  • They manufacture urine to filter out substances that the body does not need.
  • They also take nutrients and other substances from the urine and return them to the blood.

Urine is manufactured in the kidney’s renal tubules. There are approximately one million of these in each kidney. The raw material the body uses to manufacture urine is filtered blood serum, which is the plasma portion of the blood (minus proteins and blood cells).

  • The renal tubules process the filtered blood serum and remove the substances that will become urine
  • These tubules lead into collecting ducts.
  • These ducts empty the urine into small chambers referred to as renal calyces.
  • The calyces funnel the urine into the renal pelvis, a basin-shaped cavity at the base of each kidney.


The ureters are tubular organs that lead from the renal pelvis of the kidney to the bladder. The ureters transport small quantities of urine when their muscular walls contract rhythmically. This pushes the urine in a wave-like fashion through the ureters from the kidneys to bladder.


The bladder is a storage organ for urine. The bladder wall has the capacity to stretch like a balloon, enabling the bladder to expand as the volume of urine increases.

When enough urine is in the bladder, receptors that respond to the stretch in the bladder wall will send electrical signals to the brain. This creates the need to urinate.


The urethra is a tubular organ that transports urine from the bladder to the outside of the body.

  • In men, the urethra runs through the penis.
  • In women, the urethra has its own opening within the vagina

Inside the body, the urethra is surrounded by a muscle that a person can control. This muscle must relax in order for urination to occur.

How Do Kidney Stones Form?

There are several conditions that can contribute to the formation of kidney stones:

  • A high concentration of stone-forming mineral salts in the urine. When high levels of stone-forming substances such as calcium oxalate, calcium phosphate, or struvite are present in the urine, one or more crystals may form and become trapped within the urinary tract. The crystal may attract other crystals and bind together with them, growing into a stone.
  • An uneven balance of acid in the urine. The acidity or alkalinityof the urine affects the ability of stone-forming substances to remain dissolved. Some types of stones will form in acidic urine; others will form only in alkaline urine.
  • A lack of substances in the urine that prevent the growth of crystals. Normally, substances that inhibit the formation and growth of crystals – such as pyrophosphates, citrates, and magnesium – are present in the urine. A decrease in or absence of these substances may cause a stone to develop.

Why Do Kidney Stones Form?

A variety of factors can create the conditions that allow kidney stones to form. These factors include:

  • Some disturbances in the body’s metabolism
  • Certain inherited defects
  • Abnormalities within the body

Sometimes, however, it’s impossible to determine why a kidney stone has developed.

Each type of stone has its own requirements for formation.

Calcium stones form from the following:

  • Most calcium stones form for unknown reasons, although a genetic basis is suspected.
  • Certain foods can upset the balance of acid in the urine.
  • Cancer can cause the body to produce an abnormally large amount of parathyroid hormone, which regulates calcium levels in the body. High levels of this hormone can break down bone and releases too much calcium into the blood. As a result, calcium saturates the urine.

Uric acid stones form from the following:

  • Gout, the result of a genetic defect, is a disease that increases the body’s production of uric acid. High levels of uric acid in the urine can cause stones to form.
  • An inherited tendency can lead to the development of this type of stone, although the specific reason is unknown.
  • Certain gastrointestinal conditions, such as ulcerative colitis, also can lead to the formation of uric acid stones.

Cystine stones can form from high amounts of cystine in the urine, the result of a rare in inherited abnormality.

Struvite stones may form in the kidney or bladder as a result of infection from certain bacteria.

Where Do Kidney Stones Form?

Stones may form in most portions of the urinary tract, including the kidneys, ureters, and bladder.

Upper Urinary Tract Stones

Upper urinary tract stones are formed in the parts of the kidneys that play a role in forming or draining urine. Stone formation can occur in:

  • The renal tubules, which are the chemical factories that manufacture urine
  • The calyces, which are the chambers that drain urine from the collecting ducts at the ends of the renal tubules
  • The pelvis of the kidney, the large basin into which the urine collects prior to its journey through the ureters to the bladder

Upper urinary tract stones are most commonly found among people in the United States and in other technologically developed countries.

Lower Urinary Tract Stones

These stones are formed in the ureters or bladder. The stone may have either:

  • Originated in the kidneys and traveled to the lower urinary tract before continuing to grow
  • Formed directly in the ureter or bladder as a result of crystal formation in the urine

Lower urinary tract stones are most common among people in developing countries.

Need To Know:

Most kidney stones are very small and are readily passed from the body during urination. However, some large stones can block the drainage of urine from the kidneys.


What Are The Symptoms Of Kidney Stones?

Kidney stones that are above the pelvis of the kidney (the basin-shaped cavity at the base of each kidney into which urine is funneled) usually do not cause symptoms.

Symptoms often occur when a stone migrates into the ureter, the tube that carries urine from the kidney to the bladder, and prevents the drainage of urine from the kidney.

When stones are present in the ureter, a person may experience the following symptoms:

  • Pain. Pain is the major symptom of a kidney stone. A cramping pain (called renal colic) may be felt as the muscular wall of the ureter contracts in an attempt to push the stone to the bladder. The pain may be on the side of the abdomen or in the middle of the abdomen (if the stone is at the beginning of the ureter). It also may travel into the groin (if the stone is lower in the ureter). In some cases, the pain is severe enough to require medication.
  • Nausea and vomiting. These symptoms often accompany severe pain caused by a kidney stone.
  • Blood in the urine. A person may be able to see blood in the urine, or it might be detected through a laboratory test. The presence of blood is the result of damage to the lining of the ureter or tissue damage inside the kidney.
  • Increase in frequency or urgency of urination, or the inability to urinate. These symptoms, which impact the normal ability to urinate, often occur as a stone passes from the end of the ureter into the bladder.

There are other possible consequences of kidney stones. Partial or complete obstruction of a kidney by a stone may lead to a backup of urine in the blood, along with its potentially toxic component, urea. If this happens, the kidney may suffer damage to its tubules (the microscopic chemical plants that manufacture urine) and to their associated blood vessels.

Need To Know:

Although urinary tract infection is usually not a direct consequence of stone disease, the presence of a urinary tract infection can increase the severity of stone disease and make treatment more difficult.

How Are Kidney Stones Diagnosed?

The doctor will make a diagnosis of kidney stones with:

Clinical History

The doctor will ask questions in order to determine a person’s clinical history, which can help to establish the cause of stone formation. The doctor will ask about:

  • Lifestyle
  • Diet
  • Fluid intake
  • Past experience with kidney stones
  • Family history of kidney stones

Physical Examination

A physical examination can reveal conditions that place a person at higher risk for stone formation. These include:

  • Specific diseases and medical conditions
  • Certain injuries
  • Recent immobilization
  • Abdominal scars, which may be indications of previous surgery

Laboratory Evaluation

The person’s blood and urine will be studied to measure the levels of calcium, electrolytes, uric acid, and other components. In addition, the acidity of the urine is checked. When possible, a kidney stone itself will be analyzed to determine the type of stone so that the appropriate treatment can be planned.

X-ray Evaluation

X-rays can be used to identify the location of an obstruction and may even help determine the type of stone.

How Are Kidney Stones Treated?

Kidney stones may be treated with:

Extracorporeal Shock Wave Lithotripsy (ESWL)

ESWL focuses high-energy shock waves from a source outside the body and uses this energy to crush the stone into tiny pieces. These pieces are then small enough to pass out of the body during urination.

  • Shock waves created by high-voltage discharges are focused on the kidney with the stone.
  • The waves are transmitted through water. This is done either by placing the person’s lower body in a tank of water or by positioning a water-filled cushion between the person and the source of shock waves.
  • These shock waves do not damage the surrounding portions of the body.
  • Most stones are reduced to a powdery substance following multiple shock-wave discharges.

ESWL is the treatment of choice under the following circumstances:

  • People with just one stone, or those who have had ongoing problems with kidney stones, as long as the stones are no larger than three centimeters.
  • People who may not be able to tolerate open surgery.
  • People with certain health conditions, such as hypertension, breathing disorders, heart disease, and diabetes.

ESWL is most effective when treating stones smaller than three centimeters. It has best results when a stone is smaller than one centimeter in size and is located in the pelvic portion of the kidney. In these cases, the success rate is around 90 percent.

After ESWL, between 65 and 75 percent of individuals will no longer have kidney stones. The success rate is related to the size of the stone and the degree to which it can be crushed. If stone fragments remain in the urinary tract, there’s a greater chance that new stones will form.

The effectiveness of ESWL also is related to the type of stone.

  • Uric acid stones and certain types of calcium stones are easily eliminated through urination after they are crushed.
  • Other types of calcium stones do not fragment easily and their stone-free success rate is only slightly more than 40 percent.
  • Small cystine stones break up easily, but most large ones are difficult to shatter.
  • When people with staghorn stones were treated with ESWL, the stone-free success rate at the end of six months was less than 50 percent, and over 60 percent of them needed to be treated again.

Problems can also occur when stone fragments remain after treatment, because of the likelihood that another stone will form.

Complications of treatment with ESWL may include blood in the urine and abdominal discomfort for several days. A severe cramping pain may occur as shattered stone fragments rub against the inside walls of the urinary tract on their way out of the body. However, the recovery time is fairly short.

Percutaneous Nephrolithotripsy

In this procedure, performed in an operating room after a person has been given anesthesia, a small incision is made in a person’s flank. The surgeon guides a special scope to the kidney and punctures it. Using the pathway created, the surgeon inserts a small instrument into the kidney to break up the stone and remove the stone fragments.

This technique can be used to remove large stones and staghorn stones.

Laser Lithotripsy

With laser lithotripsy, a small instrument is inserted into the urethra and snaked into the ureter containing the stone. Focused laser energy is used to fragment the stone.

Other Methods

There are several other stone-removal techniques aside from lithotripsy. These procedures include percutaneous nephrolithotomy, uteroscopic stone removal, and open surgery.

  • Percutaneous nephrolithotomy: The surgeon makes a small incision in the back and uses a special instrument to tunnel directly into the kidney. A nephroscope is then placed into the kidney and used to locate and remove the stone. Larger stones may require the use of ultrasonic or other forms of energy to fragment the stone into manageable pieces for removal.

The advantage of this procedure over lithotripsy is the physical removal of the stone fragments rather than relying on their natural passage from the kidney to the outside. This treatment is often used when the stone is large or in a location that does not permit the effective use of ESWL.

Uteroscopic stone removal: The surgeon passes a small fiber-optic instrument called a ureteroscope through the urethra and bladder and then into the ureter. The stone is then located and removed with the use of a special cage-like tool, or it is shattered with an instrument that produces a shock wave. A small tube called a stent is left in the ureter for several days to promote healing of this portion of the urinary tract. This technique is used when the kidney stone is located in the middle or lower portions of the ureter.

  • Open surgery: In this procedure, performed in an operating room after a person has been given anesthesia, the surgeon makes an incision in the skin and opens the pelvis of the kidney or the ureter so that the stone can be manually removed. Because open surgery is a major operation, recovery may require four to six weeks.

Nice To Know:

The success rate of open surgery for staghorn stones is between 90 and 95 percent.

Need To Know:

Surgery may be necessary to remove a kidney stone if it:

  • Damages kidney tissues or causes ongoing bleeding
  • Causes a long-lasting or recurring urinary tract infection
  • Blocks the flow of urine and threatens kidney damage
  • Causes severe abdominal pain
  • Can’t be treated with lithotripsy and other less-invasive techniques
  • Significantly grows in size, causing various complications

Need To Know:

Some people with kidney stones may need treatment for related conditions.

For example, calcium stones are sometimes formed when the body has higher-than-normal concentrations of the hormone from the parathyroid gland, a condition known as hyperparathyroidism. This hormone is called parathyroid hormone (PTH). PTH causes an increase of calcium in the blood, which in turn increases the concentration of calcium in the urine. When abnormally high, it presents a higher risk for stone formation.

Therefore, people with calcium stones and hyperparathyroidism may need to have their parathyroid glands surgically removed. This should eliminate the future formation of calcium stones.

How Can Kidney Stones Be Prevented?

Part of the treatment of kidney stones involves preventing them from happening again. Preventive measures include:

Drinking A Large Amount Of Water

Drinking large volumes of water each day will dilute the mineral or stone-forming salts in the urine. Many experts advise people who are prone to kidney stones to drink 12 eight-ounce glasses of water a day. Stones cannot form in urine that is diluted.

Changes In Diet

Because calcium stones are the most common type of kidney stone, some experts recommend a low-calcium and low-oxalate diet.

  • Foods high in calcium include dairy products.
  • Foods rich in oxalate include colas, chocolate, peanuts, leafy vegetables, and tea.

Restricting these foods in the diet should lower the concentration of calcium and oxalate in the urine.

In many cases of uric acid stones, a diet low in animal proteins is recommended. Foods that are high in purines, which contribute to uric acid stones, include poultry and red wine.


Even with careful regulation of water intake and diet, stones still may form. But there are some medications that can help prevent this.

These medications can reduce the level of stone-forming chemicals such as uric acid, calcium, oxalate, or cystine in the blood. They also can inhibit an enzyme required by the bacteria that cause struvite stones to form. Other medications can be used for relief of pain from kidney stones.

The following table provides an overview of selected medications and their uses in reducing the formation of kidney stones or their pain symptoms.

Drugs Used To Control The Formation Of Kidney Stones And Reduce Kidney Pain:

Name of Medication

What it’s for

General Information


Calcium reduction (for calcium stones)

This diuretic helps the body reabsorb calcium from the urine back into the blood. This reduces the amount of calcium in the urine and helps prevent calcium stones. People who take this may have to reduce their intake of sodium (salt), because sodium may reduce its effectiveness.

Sodium cellulose phosphate

Calcium reduction (for calcium stones)

Binds calcium in the intestine and prevents it from leaking into the urine.

Oral calcium supplement

Reduces oxalate in the body (for calcium oxalate or calcium oxalate and phosphate stones)

Prevents absorption of oxalate into blood but requires careful supervision and cannot be used by people with kidney problems.


Uric acid reduction (for uric acid stones)

Used primarily to reduce uric acid in the urine for people whose body can’t process uric acid effectively.

Polycitra K

(potassium citrate)

Uric acid reduction (for uric acid stones)

Prevents uric acid from crystallizing in urine.


Cystine reduction (for cystine stones)

This drug increases the ability of cystine to dissolve in water, thereby reducing the likelihood of forming stones. People who take this need to increase their water intake.


Struvite reduction (for struvite stones)

Inhibits an enzyme required by the bacteria that promote the growth of these stones. Side effects are potentially serious.


droxamic acid (AHA)

Struvite reduction (for struvite stones)

Used with long-term antibiotic drugs, AHA prevents infection that leads to stone growth.


Relief of kidney pain

Within one hour after injection, pain disappears with this nonsteroidal anti-inflammatory drug (NSAID).

What Is The Outlook For People With Kidney Stones?

In recent years, there have been dramatic improvements in how kidney stones are treated.

Kidney stones now can be broken into tiny pieces and eliminated from the body without the need for any type of surgery. Avoiding traditional surgery means faster healing time, shorter hospital stays, and reduced medical expenses.

Furthermore, stones can be prevented with medications and the careful regulation of water intake and diet. With careful management and attention to prevention techniques, only one in 10 people who have had a kidney stone will actually have another.

Kidney Stones: Frequently Asked Questions

Here are some frequently asked questions related to kidney stones.

Q: I heard that where I live could affect whether I develop kidney stones. Is this true?

A: Kidney stones do occur more frequently in hot climates. In fact, a certain area in the southern part of the U.S. is dubbed the “stone belt” because kidney stones are so common, presumably because the weather is hotter and the stones are linked to dehydration.

Q: My doctor diagnosed a kidney stone but seems to think that it will pass by itself. How long does this usually take?

A: Most small stones pass through your body by themselves within hours or a few days. To help this process, your doctor will advise you to drink a lot of fluids and may suggest a special diet.

Q: What is the average size of a kidney stone?

A: A kidney stone is a solid lump that can be as small as a grain of sand or as large as the size of a golf ball.

Q: Is it safe to let a kidney stone go without treatment?

A: Not all kidney stones need treatment. If a stone is causing no symptoms, is not having any effect on the urinary tract, and is not likely to cause problems in the future, it may be left untreated and followed for future changes. If a stone is causing no symptoms and is small enough to probably pass by itself if it moves, it may be safely observed and not treated. However, some jobs require the worker to be free of stones (for example, airline pilots), and some people may travel to or live in remote areas where it is difficult to get medical care.

Q: When can I return to normal sexual activity after lithotripsy?

A: In general, sexual activity may be resumed when the person is feeling well enough not to need pain medication, is eating and taking liquids normally, and has no visible blood in the urine.

Q: How can I reduce the pain caused by the repetitive appearance of kidney stones?

A: This pain, which is referred to as renal colic, can be relieved with a strong pain medication. Aspirin and other over-the-counter pain remedies are ineffective. If you are experiencing pain from a kidney stone, go immediately to the nearest emergency room or walk-in medical center available so that you can receive prompt and effective therapy.

Q: Is shock-wave treatment painful?

A: This depends on the size and density of the kidney stone and the energy of the shock waves. In some cases, a person will receive an anesthetic to control pain.

Q: Do small retained fragments of kidney stones after lithotripsy increase the risk of stone recurrence?

A: Leftover stone fragments do appear to grow faster the usual stone recurrence rate. So if a person is not stone-free after lithotripsy, new stones may form quicker than they would in an untreated person.

Q: Will I require further treatment after my kidney stone is eliminated?

A: Lifetime follow-up with regular visits to your doctor are important to ensure that kidney stones are controlled and do not return or grow back. These follow-up visits may require additional x-rays, blood tests, or urine analysis.

Q: How important is diet in preventing recurrence of kidney stones?

A: The most important thing you can do to prevent kidney stones is to drink a lot of water each day – 12 eight-ounce glasses – to dilute your urine. Depending on the nature of the kidney stone, your doctor may provide you with information on avoiding certain foods that may increase your risk for stones in the future. Your doctor may suggest that you consult with a dietitian to help further reduce risk factors in your diet.

Kidney Stones: Putting It All Together

Here is a summary of the important facts and information related to kidney stones.

  • Kidney stones are fairly common; 10 percent of all people will experience a kidney stone at some time during life.
  • Kidney stones are accumulations of mineral salts and other substances that form solid masses of various sizes within the kidneys or other portions of the urinary tract.
  • Calcium stones are the most abundant type of kidney stones.
  • Conditions that contribute to the formation of kidney stones include a high concentration of stone-forming substances in the urine, an imbalance of acid in the urine, and a lack of substances help prevent the growth of crystals in the urine.
  • Most stones are formed in the kidneys, although some stones can form in the ureters or bladder.
  • The symptoms of kidney stones may include excruciating pain, nausea and vomiting, blood in the urine, and increase in frequency or urgency to urinate.
  • The diagnosis of kidney stones depends on a physical examination, a clinical history, a laboratory evaluation of blood and urine, and, in some cases, x-rays.
  • The treatment of kidney stone disease is primarily based on alternatives to open surgery such as extracorporeal shock wave lithotripsypercutaneous ultrasonic lithotripsy, and laser lithotripsy.
  • Preventing kidney stones involves increasing the amount of water you drink, avoiding certain foods, and possibly taking medication.

Kidney Stones: Glossary

Here are definitions of medical terms related to kidney stones.

Acidity: A condition in which the urine becomes more acid than normal.

Alkalinity: A condition in which the urine becomes more alkaline, and consequently less acid, than normal.

Amino acids: Chemical compounds that are the main components of protein and are used by the cells of the body to support life.

Antibiotic: A chemical agent, derived from a microorganism or synthetically, used to treat bacterial infections.

Bladder: The muscular sac within the abdomen that stores urine until it can be passed from the body.

Calcium stone: A kidney stone made primarily of calcium, either in the form of calcium oxalate, calcium phosphate, or a combination of the two.

Calyces: Small chambers into which urine is drained from the collecting ducts in the kidneys.

Cystine stone: A soft kidney stone composed primarily of the amino acid cystine.

Diuretic: A drug that promotes the formation and excretion of urine.

Enzyme: In the body, any protein that speeds up the rate of a chemical reaction.

Extracorporeal shock wave lithotripsy (ESWL): A procedure for the pulverization of kidney stones. Shock waves created by high-voltage discharges are focused on the stone in the kidney.

Kidneys: The two urinary organs in which urine is manufactured.

Kidney stone: An accumulation of mineral salts and other substances that form a solid mass of various sizes within the kidney.

Lithotripsy: The crushing of a stone within the urinary system, followed by removal of the fragments, a procedure that may be done either noninvasively (without a surgical incision) or with minimally invasive techniques.

Laser: A source of intense radiation of the visible, ultraviolet, or infrared portions of the electromagnetic spectrum.

Laser lithotripsy: A minimally invasive surgical technique that uses focused laser energy to fragment a stone. It involves inserting a small instrument into the urethra and snaking it through the urinary tract to the ureter with the stone.

Lower urinary tract stone: A stone that forms or exists in the ureters or bladder.

Metabolism: The chemical processes in the body that promote growth, generate energy, eliminate waste, and perform other functions.

Mineral salt: An inorganic metallic substance occurring naturally in the earth’s crust that is compounded with another inorganic nonmetallic substance to form a salt.

Nephroscope: A fiber-optic instrument that is used specifically for the disintegration and removal of kidney stones.

Percutaneous: A procedure performed through a small opening made in the skin.

Percutaneous ultrasonic lithotripsy: A minimally-invasive procedure that uses the energy of ultrasound to shatter kidney stones, the fragments of which can then be easily removed.

Radiography: The production of shadow images on photographic plates through the action of high-energy ionizing radiation.

Renal: Of or pertaining to the kidney.

Renal colic: Sharp, severe pain in the lower back, over the kidney, radiating forward into the groin.

Renal pelvis: The basin at the base of the kidney that drains urine from the renal calyces and transports urine into the ureter, with which it connects.

Renal tubules: The microscopic chemical factories in the kidneys that manufacture urine from filtered blood serum, at the same time conserving essential nutrients and other substances required by the body.

Staghorn stone: An irregularly shaped kidney stone that occupies most or all of the renal pelvis and has horn-like projections on the outside.

Stent: A tube-like device that is used to support an opening in a tubular organ in order to increase its diameter or prevent its collapse.

Struvite stone: A stone primarily composed of a combination of ammonium and magnesium phosphate, forming hard crystals identical to struvite rocks.

Upper urinary tract stone: A stone that exists in some portion of the kidney.

Ureter: One of a pair of tubes, about one foot long, that carries urine from each kidney to the bladder.

Urethra: A small tubular organ that drains urine from the bladder to the outside of the body.

Uric acid stone: A type of kidney stone whose main ingredient is uric acid, a product of protein metabolism that is present in blood and excreted in urine.

Urinary tract: All organs and ducts involved in the secretion and elimination of urine from the body.

Urinary tract infection: An infection, usually by bacteria, in one or more organs of the urinary tract.

Urination: The act of passing urine to the outside of the body.

Urine: The fluid secreted by the kidneys, transported by the ureters, stored in the bladder, and voided through the urethra.

Kidney Stones: Additional Sources Of Information

Here are some reliable sources that can provide more information on kidney stones. Sponsored by the National Institute of Health, this Web site presents health information on kidney diseases including a dictionary, online articles about kidney diseases, and easy-to-read publications. This Web site provides links to many health sites which discuss treatment, prevention, and related topics. By clicking on “FAQ about kidney stones,” the user can obtain basic information about kidney stones.

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