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Kidney Stones Renal Calculi

Most kidney stones pass spontaneously from the kidney or renal pelvis through the ureter. Stones can cause substantial pain if they become lodged in the ureter

What is it?

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 account 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 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.

What Causes It?

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.

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-ammoniumphosphate 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 (see Gout).

Prevention

  • Drink at least eight to 10 cups of water a day, and eat a healthy, well-balanced diet.
  • 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.
  • 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.

Diagnosis

  • Patient history and physical examination.
  • A blood sample to measure calcium and uric acid levels.
  • Urine culture and examination for cells and crystals.
  • 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.
  • Noncontrast CT (computed tomography) scan or abdominal x-rays, following injection of an iodine based dye into the kidneys (pyelography).
  • Laboratory analysis of the chemical content of any stone that is passed and captured.

How to Treat It

  • To encourage a small stone to pass, drink at least three liters 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.
  • Larger stones can be pulverized with a treatment called extracorporeal shock-wave lithotripsy, which aims concentrated bursts of sound waves at the stones. The tiny fragments then pass into the bladder and are excreted.
  • Abdominal surgery may be performed to remove the stone.
  • 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.

When to Call a Doctor

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