precise cause of kidney stones is still not fully understood but
many theories exist. Urine contains substances known to form
stones and to prevent stones. High levels of
compounds and elements known to cause stones include calcium, uric
acid, phophate and oxalate. In fact, urine often holds larger
amounts of these substances than can normally be held in the same
volume of pure water. Therefore, calcium salts and uric acid
can easily precipitate into crystals which can grow into larger
calcium and uric acid stones. When urine volume is low, the
relative concentrations of these substance will be even higher which
significantly increase the risk for stone precipitation. The urine also contains substances which
are known to prevent stone formation, such as magnesium, citrate and
Urine studies measure levels of calcium, phosphate, uric acid, and
oxalate to determine the
cause of a particular person's kidney stones.
These levels should not be used alone to determine the cause.
Further specialized tests should be done by phsyicians
experienced in analysis of supersaturations of calcium oxalate,
calcium phosphate, and uric acid. Supersaturations measures the interactions of the different urinary elements with
each other. The testing becomes even more complicated
when pH, ammonium, sodium, urea and sulfate measurements are
performed to determine the metabolic effects of diet on changes in urine
composition. These urinary changes often contribute to an
individual's propensity to form stones.
In addition to the
above testing. Physicians should measure urinary citrate
and magnesium levels. These are known to prevent kidney stone
formation. In some the cause of low citrate and magnesium can
be determined from the patient's history, physical exam, and analysis
of blood and urine studies. Low citrate levels can be a sign
of renal tubular acidosis (RTA), while low magnesium can can occur
with malnutrition or diuretics (water pills).
In conclusion, the
causes of kidney stone formation are multifactorial in most
individuals. A physician experienced in kidney stone care and
prevention can integrate the information from urine and blood tests
to determine the most likely causes. The important point, is
that there is often more than one cause in each person. Proper
testing and analysis is critical in order to tailor a medical and dietary regimen
particular to each person.