Renal calculi

Kidney Stones, Urinary Calculi

What is Renal calculi?

Renal calculi are stones in the kidneys or ureters that have been formed by precipitation from a substance in the urine. Although their composition is sometimes due to a specific cause, in the majority of cases there is no identifiable underlying cause. Because concentrated minerals in the urine can crystallize and form hard stones, especially when there is insufficient fluid in the urinary tract, mild chronic dehydration may play a part in stone formation.

Approximately 70% of kidney and ureteral stones are composed mainly of calcium oxalate and/or phosphate. Oxalate is naturally present in the urine as an end product of body metabolism. Higher levels of oxalate in the urine may be the result of a diet high in oxalic acid (rhubarb, leafy vegetables, coffee). When combined with calcium, oxalate forms a salt that dissolves poorly. Therefore, an abnormally high level of oxalate in the urine encourages stone formation. Calcium stones may also be the first evidence of metabolic disturbances associated with hyperparathyroidism.

Approximately twenty percent of renal calculi are linked with chronic infections of the urinary tract. Bacterial action on urea (a substance in urine) results in urine with a high alkaline and ammonium content. Called "infective stones," these stones are composed of a combination of calcium, magnesium, and ammonium phosphate. An infective stone may fill the entire network of urine-collecting ducts within the kidney, as well as the top part of the ureter. Another five percent of renal stones are composed of uric acid. These stones may occur in individuals with gout, some forms of cancer, and in chronic dehydration. Uncommon stones, such as those formed from the amino acid cysteine, affect individuals with particular inherited metabolic disorders.

Each year in the US, approximately 100 individuals per 100,000 are hospitalized with a ureteral calculus. Stones tend to be a recurring condition. Up to 60% of individuals treated for a stone will develop another stone within seven years. The incidence of renal stones is highest in the summer months. This may occur because sweating, caused by the warmer weather, makes the urine more concentrated.

How is it diagnosed?

History: Symptoms vary according to the site and size of the stone. Small stones in the kidney may cause no symptoms until they start to pass down the ureter. The resulting pain (renal colic) is acute, sharp, and intermittent. Starting in the flank, the pain moves toward the groin. The pain may be so severe that it causes nausea and vomiting. Blood may be noted in the urine (hematuria).

Physical exam: The individual appears to be in severe pain. Blood pressure may be elevated as a result of the pain. Tapping softly on the flank will make the pain worse. As the stone moves farther down the urinary tract, the abdomen, although soft, may be tender over the location of the stone. Pelvic and prostate exams should be normal.

Tests: Examination of the urine may reveal large numbers of red blood cells and the presence of crystals. The degree of acidity or alkalinity of the urine may indicate the type of stone involved. X-ray studies of the abdomen can identify up to 85% of renal calculi, and will show the site of the stone. An intravenous pyelogram (x-ray of kidneys after intravenous injection with contrast medium) can confirm the site of the stone and also indicate any obstruction of the urinary tract above the stone. Obstruction can also be monitored by ultrasound scanning. When a metabolic disorder is the suspected cause of the stone, chemical analysis of the blood and urine may reveal high levels of calcium, phosphate, or urate.

How is Renal calculi treated?

Renal calculus is treated with bedrest and pain relief (often using narcotic painkillers). Fluid intake is increased to encourage the passage of the stone from the kidney, through the ureter, bladder, and out through the urethra. The majority of small stones (less than five millimeters in diameter) are passed in the urine with relatively few problems.

With larger stones, or if an infection or obstruction to the urinary flow is present, surgical treatment may be needed to prevent damage to the kidney. The traditional method of removing stones from the ureter or from the junction between the ureter and kidney has been by surgery under general anesthesia (lithotomy). Distal stones in the ureter can also be crushed and removed through ureteroscopic stone extraction. A viewing tube with crushing device is passed up the urethra, bladder, and into the ureter.

Under direct vision, the stones are crushed or removed with basket forceps. In recent years, however, newer methods have evolved for removing kidney and ureteral stones. In ultrasonic or percutaneous lithotripsy, a nephroscope (telescopic viewing tube) is inserted into the kidney through a small flank incision. An ultrasonic probe, directed through the tube, breaks up the stone. Fragments of the stone are removed out through the nephroscope.

Another procedure uses extracorporeal shock wave lithotriptor (ESWL) to disintegrate kidney stones by focusing shock waves on the stone from outside the body. X-ray imaging shows the position of the stone and monitors its destruction into fine sand, which is passed out of the body in urine over the following few weeks. ESWL is used to break up smaller stones, while percutaneous lithotripsy is used to break up larger stones. A combination of the two procedures may be used to treat very large stones.

If a stone is thought to have been caused by a metabolic disorder, the individual may be prescribed a diet (and possibly drugs) to lower the urine content of the substance from which the stone was formed. Increased fluid intake may be necessary to not only dissolve existing stones, but also to help prevent recurrences. Stones associated with hyperparathyroidism may be treated by removing the parathyroid tumor responsible for the condition.


  • Pain relievers.
  • Antispasmodics to relax the ureter muscles and help the stone pass.
  • Depending on the type of stone (calcium-containing, struvite stones, cystine stones, uric acid or other composition), medication may be prescribed that will stop the growth of existing stones or new stones. This often involves a prolonged program, and your compliance is important.
Information Brand Generic Label Rating
Prednisone Deltasone Prednisone
Motrin Ibuprofen
Aleve Naproxen
Microzide Hydrochlorothiazide
Zyloprim Allopurinol
Ureteral Stones
Flomax Tamsulosin


  • If you know you have kidney stones, avoid situations in which a sudden pain might cause danger, such as climbing ladders or working on roofs or girders.
  • During a kidney-stone episode, stay as active as possible. Don't go to bed. Activity may help the stone pass.


  • If the stone proves to be calcium or phosphorus, avoid products made with milk, chocolate and nuts.
  • If the stone is a phosphate, an acid-ash diet will keep the urine slightly acid.
  • If the stone is a urate or cystine stone, an alkaline-ash diet will keep the urine slightly alkaline.
  • For all types of stones, drink at least 13 glasses of fluid daily. Most of the fluid should be purified water.
  • Low-fat, high-fiber diet recommended.

What might complicate it?

Renal calculi may be associated with recurrent episodes of urinary tract infection. Any obstruction to urine flow may result in rapid kidney damage or severe kidney infection (pyelonephritis).

Predicted outcome

In most cases, the stone passes without incidence. However, stones tend to be a recurrent problem. Approximately 60% of individuals treated for a stone will develop another stone within seven years.


Conditions with similar symptoms include pyelonephritis, kidney tumor, retroperitoneal bleeding, back strain, cholecystitis, appendicitis, and vertebral compression fracture.

Appropriate specialists

Urologist and nephrologist.

Notify your physician if

  • You or a family member has symptoms of a kidney stone.
  • Temperature rises to 101°F (38.3° C).
  • Symptoms of a kidney infection develop (stinging, burning on urination or a frequent urge to urinate).

Last updated 6 October 2015


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