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CALCIUM OXALATE STONES

How common are calcium oxalate stones?
In the United States, the incidence of urinary stone disease is estimated to be 0.1-0.3%. Therefore, 240,000-723,000 Americans suffer a metabolic stone event each year, with men more frequently affected than women. The prevalence of stone disease is estimated to be 5-10%, meaning that in the United States alone, 12-24 million people will develop a stone at some time during their life.
 
Describe the radiographic characteristics of calcium oxalate stones.
On a plain radiograph, calcium oxalate stones are opaque, with a radiodensity similar to that of iodinated contrast. Therefore, after contrast is administered for a urogram or during a retrograde study, the stone may be obscured. Ultrasound and computed tomography can identify stones, although these studies cannot distinguish calcium oxalate calculi from stones of other composition.
 

,What causes calcium oxalate stones?

In simplest terms, they form when the urine is supersaturated with calcium oxalate-i.e., when the concentration of calcium oxalate in the urine exceeds its solubility.
 
. What are some of the environmental risk factors?
A low urine volume is clearly associated with an increased risk of stones. Though not well documented, there does appear to be an increased risk for patients in hotter climates or working conditions, at least during an initial acclimatization period.
 
Is it true that people with calcium oxalate stones should avoid dairy products?
Probably not. Although it might seem reasonable that dairy products, with their relatively high calcium content, might predispose to calcium oxalate stones, there is little scientific evidence to support that concept. In fact, in otherwise healthy people, a diet high in calcium may provide protection from these stones. One possible explanation is that the dietary calcium is needed to find oxalate in the intestinal tract, which then prevents absorption of the oxalate.

 
What dietary advice should be given to prevent calcium oxalate stones?
A high fluid intake is most important, as it will increase urinary volume and decrease the concentration. of calcium oxalate. A diet low in oxalates is more reasonable than a calciumrestricted diet. Tea, nuts, and some green leafy vegetables are high in oxalates. Studies have also shown a benefit in restriction of salt and fat intake as well as increased dietary fiber. Actually, a healthy diet in general is a stone-prevention diet.
 

When should a patient be evaluated for metabolic risk factors?
There is some difference of opinion here, but certainly any patient with recurrent calcium stones should be offered a metabolic evaluation. Even a single kidney stone event should prompt metabolic evaluation when it occurs in a child.
 
What are these studies looking for?
The most frequent cause of recurrent calcium oxalate stones is "idiopathic" hypercalciuria. A reasonable definition for this is a 24-hour urinary calcium excretion exceeding 300 mg in men or 250 mg in women~ although others define hypercalciuria as 24-hour urinary excretion of> 4 mg Ca/kg. The uric acid level is also important even for calcium stones, as hyperuricosuria is clearly associated with an increased risk for calcium oxalate stones. The citrate levels are important, as hypocitraturia is a well-known risk factor for recurrent calcium stones and may also be associated with renal tubular acidosis. Sodium excretion is an important marker of sodium intake, and elevated salt intake is associated with increased calcium excretion.
 

Can any treatment prevent stones?
That depends on the result of the metabolic evaluation. Hypercalciuria is usually treated with diuretics that decrease urinary calcium excretion. The most frequently used and perhaps best studied one has been hydrochlorothiazide, which is very effective in these cases. Patients with hyperuricosuria may benefit to some degree from a purine-restricted diet, though dietary restriction alone may not be adequate. In those cases, allopurinol is used to decrease urinary uric acid excretion and has proven effective in then reducing the recurrence rate of calcium oxalate stones. Patients with hypocitraturia can be treated with citrate supplements. Patients with renal tubular acidosis require large doses of alkalinizing agents.
 
 

Is it true that some calcium stones can be dissolved?
No.

 
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