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What is a kidney stone?

Kidney stones (calculi) are hardened mineral deposits that forms in a kidney when substances that are normally found in the urine become highly concentrated. They originate as microscopic particles or crystals and develop into stones over time.
The medical term for this condition is nephrolithiasis, or renal stone disease.
A stone may stay in the kidney or travel down the urinary tract.A ureteral stone—or ureterolithiasis—is a kidney stone found in the ureter.

Kidney stones vary in size. A small stone may pass on its own, causing little or no pain. A larger stone may get stuck along the urinary tract and can block the flow of urine, causing severe pain or bleeding.

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What is the urinary tract?

The urinary tract is the body’s drainage system for removing wastes and extra water. The urinary tract includes two kidneys, two ureters, a bladder, and a urethra. The kidneys are two bean-shaped organs, each about the size of a fist. They are located near the middle of the back, just below the rib cage, one on each side of the spine. Every day, the two kidneys process about 200 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra water. The urine flows from the kidneys to the bladder through tubes called ureters. The bladder stores urine until releasing it through urination. When the bladder empties, urine flows out of the body through a tube called the urethra at the bottom of the bladder.

Kidney anatomy

Drawing of the urinary tract with labels to the kidneys, bladder, ureters, and urethra. Insets show a cross section of the kidney with labels to the kidney, stones, and ureter and a cross section of the bladder with labels to the ureters, stones, bladder, and urethra.
Kidney stones in the kidney and urinary tract

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Who gets kidney stones?

Anyone can get a kidney stone, but some people are more likely to get one. Men are affected more often than women, and kidney stones are more common in non-Hispanic white people than in non-Hispanic black people and Mexican Americans. Overweight and obese people are more likely to get a kidney stone than people of normal weight. In the United States, 8.8 percent of the population, or one in 11 people, have had a kidney stone

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What causes kidney stones?

Several factors increase the risk for developing kidney stones, including inadequate fluid intake and dehydration, reduced urinary volume, certain chemical levels in the urine that are too high (e.g., calcium, oxalate, uric acid) or too low (magnesium, citrate), and several medical conditions such as reflux, medullary sponge kidney, renal tubular acidosis and urinary tract infections (UTIs). Anything that blocks or reduces the flow of urine (e.g., urinary obstruction, genetic abnormalities) also increases the risk.

Chemical risk factors include high levels of the following in the urine:
  • Calcium (hypercalciuria)
  • Cystine (cystinuria; caused by a genetic disorder)
  • Oxalate (hyperoxaluria)
  • Uric acid (hyperuricosuria)
  • Sodium (hypernaturesis)
Urine normally contains chemicals-citrate, magnesium, pyrophosphate-that help prevent the formation of crystals and stones. Low levels of these inhibitors can contribute to the formation of kidney stones. Of these, citrate is the most important

The following medical conditions are also risk factors for kidney stone disease:
  • Colitis (inflammation of the colon that causes chronic diarrhea, dehydration, and chemical imbalances
  • Gout (caused by excessive uric acid in the blood) which leads to high urinary uric acid levels
  • Hyperparathyroidism (excessive parathyroid hormone, which causes calcium loss from bone)
  • Mdullary sponge kidney (MSK; a congenital kidney defect associated with urinary tract infections, low urinary citrate levels, and increased urinary calcium loss)
  • Renal tubular acidosis (inherited condition in which the kidneys are unable to excrete acid)
  • Urinary tract infections (UTIs; affect kidney function and chemistry)
A diet high in sodium, fats, meat, animal protien and low in fiber, vegetable protein, and unrefined carbohydrates increases the risk for renal stone disease.

Oxalate is found in, Red meat (beef, pork, mutton), vegetables (e.g., greens, spinach,), nuts, chocolate, coffee and strong tea.

certain medicines :

  • diuretics—medications that help the kidneys remove fluid from the body
  • calcium-based antacids
  • the protease inhibitor indinavir (Crixivan), a medication used to treat HIV infection
  • the anti-seizure medication topiramate (Topamax)

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What are the types of kidney stones?

The chemical composition of stones depends on the chemical imbalance in the urine. The five most common types of stones are comprised of calcium-calcium oxalate and calcium phosphate, uric acid, struvite, and cystine.

  • Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common. Calcium oxalate stone formation may be caused by high calcium and high oxalate excretion. Calcium phosphate stones are caused by the combination of high urine calcium and alkaline urine, meaning the urine has a high pH.
  • Uric acid stones form when the urine is persistently acidic. A diet rich in purines—substances found in animal protein such as meats, fish, and shellfish—may increase uric acid in urine. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium.
  • Struvite stones result from kidney infections. Eliminating infected stones from the urinary tract and staying infection-free can prevent more struvite stones.
  • Cystine stones result from a genetic disorder that causes cystine to leak through the kidneys and into the urine, forming crystals that tend to accumulate into stones.

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What do kidney stones look like?

Kidney stones vary in size and shape. Stones may be as small as a grain of sand or as large as a pearl. Some stones are even as big as golf balls. Stones may be smooth or jagged and are usually yellow or brown.

Drawing of three kidney stones of various shapes. The stones are labeled golf ball–sized and brown, small and smooth, and jagged and yellow.
Kidney stones vary in size and shape. These stones are not actual size.

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What are the symptoms of kidney stones?

People with kidney stones may have pain while urinating, see blood in the urine, or feel a sharp pain in the back or lower abdomen. The pain may last for a short or long time. People may experience nausea and vomiting with the pain. However, people who have small stones that pass easily through the urinary tract may not have symptoms at all.

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How are kidney stones diagnosed?

To diagnose kidney stones, the health care provider will perform a physical exam and take a medical history. The medical history may include questions about family history of kidney stones, diet, GI problems, and other diseases and disorders. The health care provider may perform urine, blood, and imaging tests, such as an x ray or computerized tomography (CT) scan to complete the diagnosis.

  • Laboratory tests : Include a urinalysis to detect the presence of blood (hematuria) and bacteria (bacteriuria) in the urine. Other tests include blood tests for creatinine (to evaluate kidney function), BUN and electrolytes (to detect dehydration), calcium (to detect hyperparathyroidism), and a complete blood count (CBC; to detect infection).
  • Imaging tests :Imaging tests used to diagnose kidney stones include ultrasound, KUB (plain abdominal x-ray), intravenous pyelogram (IVP), retrograde pyelogram, and computed tomography (CT) scan.
  • Ultrasound :This test uses high-frequency sound waves to produce pictures of internal structures (e.g., organs, kidney stones). Ultrasound can detect a dilated (stretched) upper urinary tract and kidney caused by a stone lodged in the ureter, but usually cannot detect small stones, especially those located outside the kidney. It is the preferred imaging method for kidney stone patients who are pregnant.
  • Intravenous Pyelogram (IVP): This test involves taking a series of x-rays after injecting a contrast agent (dye) into a vein. The contrast agent flows through the veins, is excreted by the kidneys, and improves the x-ray images of the kidneys and ureters. If a kidney stone is blocking a ureter, the contrast agent builds up in the affected kidney and is excreted more slowly. Most kidney stones can be precisely located using this procedure. There is a slight risk for an allergic reaction to the contrast agent during this study and overall kidney function must be normal. IVP can take a very long time if the blockage to the kidney is severe and it requires a radiologist be present.
  • Retrograde Pyelogram :A cystoscopy (i.e., a procedure in which a telescopic instrument is inserted into the bladder) is performed to locate the opening from the ureter to the bladder. The contrast agent is injected directly into this opening and an x-ray is taken to locate the kidney stone.
    This procedure eliminates the risk of an allergic reaction to the contrast agent because the dye does not reach the bloodstream, but it may require anesthesia. While a retrograde pyelogram is the most reliable method for visualizing the urinary system and detecting stones, it is generally used only when other imaging methods are inadequate or unsuccessful.
  • Computerized tomography (CT Scan) :This test uses a scanner and a computer to create images of the urinary system. It is performed quickly but may have difficulty detecting small stones located near the bladder. CT scans can also help identify other medical conditions (e.g., ruptured appendix, bowel obstruction, abdominal aortic aneurysm) that cause symptoms similar to kidney stones.

    Newer scanners do not require a contrast agent. The non-contrast CT scan is the most common imaging test used to evaluate a possible kidney stone attack. If any stones are found, a plain abdominal x-ray is also taken to determine their size, shape, and orientation. X-rays are used for follow-up studies to monitor the stones' progress.

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How are kidney stones treated?

Kidney stones are removed by various methods, depending on the nature of stones formed. The following treatments are common and effective in removing kidney stones.

  • Extracorporeal Shock Wave Lithotripsy (ESWL) Kidney stones upto 1.5 cm can be treated by this method as day care procedure without anesthesia or surgery.
  • Flexible Ureteroscopy This facility helps in diagnosis as well as treatment of kidney tumors and stones without open surgery.

Drawing of the bladder, ureter, and kidney with a cross section of a ureteroscope inserted through the bladder into the ureter, where a stone blocks urine flow. Labels point to the kidney, ureter, stone, bladder, ureteroscope, and eyepiece. Inset is a cross section of the ureter that shows a wire basket at the end of the ureteroscope capturing the stone.
Ureteroscopic stone removal

  • Keyhole Surgery for Larger Kidney stones (PCNL) Kidney stones greater than 3 cm can be removed through a small keyhole in the back.

Drawing of a kidney cross section with a kidney stone. A wire called a nephroscope is inserted through the skin into the kidney to locate the stone. A thicker probe labeled ultrasonic probe is inserted through the skin into the kidney to deliver sound waves that will break up the kidney stone.
Percutaneous nephrolithotomy

Drawing of a nephrostomy tube with the kidney, nephrostomy tube, and urine collection bag. The curled end of the nephrostomy tube is within the left kidney. The nephrostomy tube exits the body through the skin. A urine collection bag is connected to the external end of the nephrostomy tube.
Nephrostomy tube

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How are kidney stones prevented?

Prevention of renal stone disease depends on the type of stone produced, underlying urinary chemical risk factors, and lifestyle modifications such as increased fluid intake and changes in diet.
Orange juice and lemonade with real lemon juice are good sources of citrate and may be recommended as an alternative to water. Limiting meat, salt, and foods high in oxalate (e.g., green leafy vegetables, chocolate, nuts) in the diet may also be recommended. Medication may be prescribed and treatment for an underlying condition that causes renal stone disease may be necessary.

Calcium Oxalate Stones

  • reducing sodium
  • reducing animal protein, such as meat, eggs, and fish
  • getting enough calcium from food or taking calcium supplements with food
  • avoiding foods high in oxalate, such as spinach, rhubarb, nuts, and wheat bran

Calcium Phosphate Stones

  • reducing sodium
  • reducing animal protein
  • getting enough calcium from food or taking calcium supplements with food

Uric Acid Stones

  • limiting animal protein

Medications

The health care provider may prescribe certain medications to help prevent kidney stones based on the type of stone formed or conditions that make a person more prone to form stones:

  • hyperuricosuria—allopurinol (Zyloprim), which decreases uric acid in the blood and urine
  • hypercalciuria—diuretics, such as hydrochlorothiazide
  • hyperoxaluria—potassium citrate to raise the citrate and pH of urine
  • uric acid stones—allopurinol and potassium citrate
  • cystine stones—mercaptopropionyl glycine, which decreases cystine in the urine, and potassium citrate
  • struvite stones—antibiotics, which are bacteria-fighting medications, when needed to treat infections, or acetohydroxamic acid with long-term antibiotic medications to prevent infection

People with hyperparathyroidism sometimes develop calcium stones. Treatment in these cases is usually surgery to remove the parathyroid glands. In most cases, only one of the glands is enlarged. Removing the glands cures hyperparathyroidism and prevents kidney stones.

24-Hour Urine Test :Effective preventative measures are based on the patient's chemical risk factors, which can often be uncovered with a 24-hour urine test and a blood test.
  • The patient strains their urine to collect stones for chemical analysis.
  • The physician performs a blood test to evaluate the serum calcium, uric acid, phosphate, electrolytes, and bicarbonate content.
  • Urine is collected during a 24-hour period and analyzed for calcium, citrate, uric acid, magnesium, phosphate, sodium, oxalate, pH (acid level), and total volume.
  • The physician evaluates the data and recommends dietary modifications, supplements, and medications to minimize the risk for developing kidney stones. The 24-hour urine test may be repeated several months after treatment has begun to determine the success of the therapy and any adjustments that should be made. Long-term strict compliance and periodic retesting will substantially reduce the risk for future stone formation.

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Points to Remember

  • A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated.
  • Kidney stones are one of the most common disorders of the urinary tract.
  • Certain foods may promote stone formation in people who are susceptible, but scientists do not believe that eating any specific food causes stones to form in people who are not susceptible.
  • People with kidney stones may have pain while urinating, see blood in the urine, or feel a sharp pain in the back or lower abdomen. However, people who have small stones that pass easily through the urinary tract may not have symptoms at all.
  • To diagnose kidney stones, the health care provider will perform a physical exam and take a medical history. The health care provider may perform urine, blood, and imaging tests to complete the diagnosis.
  • Treatment for kidney stones usually depends on their size and what they are made of, as well as whether they are causing pain or obstructing the urinary tract. Treatments may include shock wave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy.
  • Kidney stones may be prevented through changes in eating, diet, and nutrition and medications.

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