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Renal calculi

Kidney stones, also known as nephrolithiases, urolithiases or renal calculi, are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. They vary in size from as small as a grain of sand to as large as a golf ball. more...

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Kidney stones typically leave the body in the urine stream; if they grow relatively large before passing (on the order of millimeters), obstruction of a ureter and distention with urine can cause severe pain most commonly felt in the flank, lower abdomen and groin.


Conventional wisdom has held that consumption of too much calcium can aggravate the development of kidney stones, since the most common type of stone is calcium oxalate. However, strong evidence has accumulated demonstrating that low-calcium diets are associated with higher stone risk and vice-versa for the typical stone former.

Other examples of kidney stones include struvite (magnesium, ammonium and phosphate), uric acid, calcium phosphate, or cystine (the amino acid found only in people suffering from cystinuria). The formation of struvite stones is associated with the presence of urease splitting bacteria (Klebsiella, Serratia, Proteus, Providencia species) which can split urea into ammonia, most commonly Proteus mirabilis.


Kidney stones are usually idiopathic and asymptomatic until they obstruct the flow of urine. Symptoms can include acute flank pain (renal colic), nausea and vomiting, restlessness, dull pain, hematuria, and possibly fever if infection is present. Acute renal colic is described as one of the worst types of pain that a patient can suffer from. But there are also people who have no symptoms until their urine turns bloody—this may be the first symptom of a kidney stone.

Diagnosis & Investigation

Diagnosis is usually made on the basis of the location and severity of the pain, which is typically colic in nature (comes and goes in spasmodic waves). Radiological imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone.

The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder—KUB. This may be followed by an IVP (Intravenous Pyelogram) which requires roughly about 50ml of a special dye to be injected into the bloodstream that goes straight to the kidneys and helps outline any stone on a repeated X-ray. Computed tomography, a specialized X-ray, is by far the most accurate diagnostic test for the detection of kidney stones.

Investigations typically carried out include:

  • Culture of a urine sample to exclude urine infection (either as a differential cause of the patient's pain, or secondary to the presence of a stone)
  • Blood tests: Full blood count for the presence of a raised white cell count (Neutrophilia) suggestive of infection, a check of renal function and if raised blood calcium blood levels (hypercalcaemia).
  • 24 hour urine collection to measure total daily urinary calcium, oxalate and phiosphate.


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Managing patients with urolithiasis over time
From American Family Physician, 10/15/04 by Bill Zepf

Up to 12 percent of the population will have a urinary tract stone at least once, and the likelihood of stone recurrence is about 50 percent. Teichman reviews the diagnostic work-up and management of patients with this common condition.

The typical presenting symptom of a renal stone is acute, colicky f lank pain that radiates to the groin. As the stone drops from the renal pelvis, down the ureter to the ureterovesical junction, most patients have dysuria, and urinary urgency and frequency. About 90 percent of patients with urolithiasis have at least microscopic hematuria.

Intravenous urography is no longer the gold standard for diagnosing urolithiasis. Unenhanced helical computed tomographic (CT) scanning has been shown to have higher sensitivity and specificity for stone detection. CT scans have the additional benefit of identifying other causes of abdominal pain when a stone is not present. Ultrasonography has much lower sensitivity for finding stones, but it is the preferred imaging modality in pregnant women.

Typically, urgent intervention is not indicated for urolithiasis, but it may be necessary if the upper urinary tract is obstructed and infected, the renal function is compromised, or there is intractable pain or vomiting. Most patients are managed expectantly with analgesics for pain relief. The author notes that no randomized studies have compared narcotics with nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief in renal colic, but they appear to have roughly equal efficacy. If an NSAID is chosen, intravenous ketorolac provides more rapid pain relief than oral dosing. The likelihood of spontaneous stone passage is directly related to the size of the stone and the time needed for passage. If no stone movement has occurred after a month, intervention is warranted because the incidence of complications (e.g., renal deterioration, sepsis, ureteral stricture) is increased.

Uric acid stones are amenable to medical management by alkalinizing the urine with oral supplements of potassium citrate, which dissolves the stone. Other metabolic factors that are associated with stone formation include low urinary volume, hypercalciuria, and hypocitraturia.

When intervention is required, shock-wave lithotripsy often is used to break up proximal ureteral stones less than 1 cm in diameter. For larger stones or those more distal in the ureter, ureteroscopy or lithotripsy may be used. Ureteroscopes with laser tips can photothermally disrupt stones. Laser stone ablation is less expensive than lithotripsy, but it is technically more demanding and time consuming.


Teichman JM. Acute renal colic from ureteral calculus. N Engl J Med February 12, 2004;350:684-93.

COPYRIGHT 2004 American Academy of Family Physicians
COPYRIGHT 2004 Gale Group

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