Uric Acid Stones form from high concentrations of
uric acid in acidic (low pH) urine. At low pH
uric acid precipitates, while at normal pH it
dissolves. In contrast to calcium stones, this type of stone
can be "dissolved" purely with medical treatment.
The cause of the elevated urinary uric acid can be multifactorial including high protein diet and
includes increasing the urine pH with
potassium citrate (making the urine less acidic) in
addition to increasing water intake. Citrate is
converted to bicarbonate, which increases urine pH.
Occasionally, allopurinol is used to decrease
production of uric acid by the body.
uric acid levels (Hyperuricosuria)
in the urine can also lead to calcium stones.
One reason may be that small uric acid crystals
form, but this is not certain. These crystals
would then form seeds on which
calcium crystals can grow. Another possibility
is that dissolved uric acid somehow causes calcium
oxalate to precipitate into crystals and stones.
In this setting (i.e. calcium stones with high urine
uric acid levles) treatement can be with either allopurinol or
occasionally potassium citrate. A low purine diet is
also an important aspect of prevention.