Encyclopedia / K / Kidney Stones

Kidney Stones

What Are Kidney Stones?

Kidney stones, also known as renal calculi, form when substances (such as calcium oxalate) in the urine concentrate and coalesce into hard, solid lumps in the kidney. Calcium-containing stones are the most common, accounting for about 70 to 80 percent of renal calculi (most of these consist of calcium oxalate or calcium phosphate). Other stones are composed of uric acid or a combination of magnesium, ammonium, and phosphate.

During the production of urine, the two kidneys regulate the fluid and electrolyte balance in the body and filter wastes out of the blood. Urine collects in the portion of the kidney known as the renal pelvis; the urine then passes from the kidney to the bladder via a narrow tube called the ureter. Kidney stones may form in the renal pelvis, then pass through the ureter into the bladder before they are eliminated from the body with the urine. Some stones are so small that they cause no symptoms and pass painlessly on their own; large stones may never leave the kidney and can be detected only if an abdominal x-ray or CT scan is taken for other reasons.

Sometimes, however, a stone enters the ureter and produces intermittent severe pain (known as renal colic) that continues until the stone has reached the bladder; this process may take a few hours or up to several days. The pain of a single attack is usually felt on only one side of the body; however, stones may recur or develop in the other kidney, causing pain on that side. Symptoms subside once the stone is passed. Recurrence is common, and treatment is aimed at relieving symptoms, dissolving or removing existing stones, and preventing recurrence. Kidney stones are common, especially among middle-aged white men.

Who Gets Kidney Stones?

People who live near large bodies of water (e.g., Great Lakes, Gulf of Mexico), those who live in "soft" water areas, those who live in warmer climates, and those who have a sibling or parent with the condition experience a higher incidence of renal stone disease.

According to the U.S. National Institutes of Health (NIH), roughly 1 person in 10 develops kidney stones during their lifetime and renal stone disease accounts for 7–10 of every 1,000 hospital admissions. Kidney stones are most prevalent in patients between the ages of 30 and 45, with men affected three times more often than women and white people more prone to attacks than African-Americans. Overall incidence declines after age 50.

At least half of those suffering a kidney stone attack will have a recurrence within five years if there is no medical intervention.


  • Intermittent pain, sometimes excruciating, beginning in the lower back below the ribs and traveling downward through the lower abdomen to the groin. Men may experience pain in the testes and penis as the stone passes.
  • Interruption of the urine stream, inability to urinate except in certain positions, frequent urge to urinate but with only small amounts of urine passed.
  • Bloody, cloudy, or darkened urine.
  • Nausea and vomiting.
  • Burning upon urination
  • Fever and chills (if a concomitant infection is present)

Causes/Risk Factors

All stones:

  • Low urine volume concentrates the urine and may lead to stone formation.
  • Hereditary factors may be associated with stone formation.
  • In some cases the cause of kidney stones is unknown.
  • Living in a hot climate may be a factor. Hot weather causes increased sweat loss and reduced urine production, so that urine contains a higher concentration of stone-producing mineral content.

Calcium stones:

  • The most common cause of calcium-containing kidney stones is increased calcium in the urine (hypercalciuria).
  • High blood calcium levels (for example, from hyperparathyroidism or vitamin D intoxication) may lead to hypercalciuria and kidney stones.
  • Irritable bowel disease, Crohn’s disease, a diet high in oxalate (found in rhubarb, spinach, and other leafy vegetables), or severe dietary calcium restriction increases the excretion of oxalate in the urine and raises the risk of calcium oxalate stones.
  • Low urine citrate can cause calcium stones.

Magnesium-ammonium-phosphate stones:

  • Urinary tract infections involving certain bacteria that break down urea may create a chemical environment conducive to kidney stone development.
  • Urea is made into ammonium and the urine is made alkaline, which may lead to magnesium-ammonium-phosphate stones.

Uric acid stones:

  • Excessively acidic urine is the most common cause of uric acid stones. High uric acid levels in the urine, sometimes associated with symptoms of gout, may also lead to their formation.

What If You Do Nothing?

Most stones are small, and are passed out in the urine without notice or pain. Large kidney stones may stay in the kidney and cause no problems. When a large stone does enter the ureter, it can cause pain that may last up to 72 hours or more and that sends many people to the emergency room. The pain stops once the stone passes into the bladder. While you may need medication to combat the pain, a stone usually passes without causing any complications. If a large stone can’t pass, however, it can block the flow of urine and cause eventual kidney damage. To prevent this, the stone may need to be removed.


  • Patient history and physical examination.
  • A blood sample to measure calcium and uric acid levels.
  • Urine culture and examination for cells and crystals.
  • Noncontrast CT (computed tomography) scan or abdominal x-rays, following injection of an iodine-based dye into the kidneys (pyelography).
  • Abdominal ultrasound—which uses sound waves that are converted into images—can be used to detect kidney stones.
  • In cases when stones recur, your doctor may ask you to collect urine over a 24-hour period in order to measure the amount of calcium, sodium, oxalate, citrate, uric acid, sulfate and/or urea nitrogen. Urine volume and pH may also be measured.
  • Laboratory analysis of the chemical content of any stone that is passed and captured.


  • To encourage a small stone to pass, drink at least three quarts of water daily to flush the stone into the bladder. Urinate through a piece of gauze or filter to trap the stone when it passes, so it can be analyzed.
  • Over-the-counter pain relievers in moderation are recommended.
  • Antibiotics may be prescribed to treat an associated bacterial infection.
  • In more severe cases hospitalization may be advised, and narcotic painkillers are prescribed to relieve pain.
  • Antispasmodic drugs may be prescribed to help the ureter muscles relax and ease passing of the stone.
  • Stones too large to pass easily can be pulverized into tiny particles with a treatment called lithotripsy. Extracorporeal shock-wave lithotripsy aims concentrated bursts of sound waves at the stones. The tiny fragments then pass into the bladder and are excreted in the urine. The procedure is not appropriate for patients with very large stones.
  • Surgery using a ureteroscope may be performed to remove the stone, especially a stone in the ureter. A thin viewing instrument is passed through the bladder and ureter to reach the stone, and the surgeon can then grab the stone with a special wire basket and pull it free. A laser can also be used to break up the stone.
  • Large or complex kidney stones may require surgery using a nephrostomy tube—a soft plastic tube that is placed in the back directly into the kidney to drain urine. This is a temporary procedure and requires subsequent treatment.
  • Surgery to remove an overactive parathyroid gland may be performed in cases where stones have resulted from hyperparathyroidism.
  • Surgery to remove the kidney may be required in extremely rare and advanced cases that do not respond to other forms of treatment. Only one kidney is necessary for normal body function; if a diseased kidney is removed, the remaining one compensates for the loss.


  • Drink at least two to three quarts of water daily (eight to 12 cups of water a day), and eat a healthy, well-balanced diet. Make sure your urine is pale yellow or almost colorless. Increase your intake of fluid in hot weather.
  • Dietary changes may be advised to prevent recurrence. Specific changes—such as avoiding sodium, animal protein, and foods containing high amounts of oxalate (found in rhubarb, spinach, leafy vegetables, and coffee)—will depend on the type of kidney stone involved.
  • It is important to note that severe dietary calcium restriction is discouraged. Recent research suggests that getting the recommended amounts of calcium may actually help prevent stones in some people.
  • Medications such as thiazide diuretics, allopurinol, sodium or potassium citrate, calcium, or magnesium may be administered to help prevent recurrence of stones. The type of medication varies according to the exact composition of the stone.
  • The doctor may prescribe potassium citrate to decrease urine acidity in those with uric acid stones. Drinking water with lemon may also help acidify the urine and reduce stone recurrence.

When To Call Your Doctor

  • Call a doctor if you develop symptoms of kidney stones.

Reviewed by Sovrin M. Shah, M.D., F.A.C.S., Assistant Professor of Urology, Icahn School of Medicine at Mount Sinai, Pelvic Medicine and Reconstructive Surgery, Sol and Margaret Berger Department of Urology, Mount Sinai Beth Israel, and Phillips Ambulatory Care Center, New York, NY. Review provided by VeriMed Healthcare Network.