The most common types of
kidney stones are composed predominantly of calcium oxalate. A
smaller proportion are composed mainly of calcium phosphate.
Many stones can be mixtures of calcium oxalate and phosphate, but
usually oxalate will predominate.
Many factors contribute
to the development of calcium oxalate stones.
Physicians perform urinary studies to analyze calcium,
oxalate, uric acid, and citrate levels and for dietary levels of
sodium and protein. There can be derangements in the
concentrations of one or more of these urine components. These tests are necessary to guide treatment
and dietary changes.
Calcium is absorbed from
the gut and stored in bone. Body levels are in part regulated by the kidney. High urine concentrations of calcium can lead
to stone formation. Causes of high urine calcium include a
genetic disorder known as familial HYPERCALCIURIA,
and also hyperparathyroidism, which is less common in young people.
The cause of
hypercalciuria appears to be multifactorial. Typically there
is increased absorbtion of calcium from the diet and/or bones with
subsequent increased calcium
excretion into the urine. Treatment is NOT
directed at lowering calcium in the diet, or absorption from the
gut. Instead, therapy is designed to decrease calcium
concentrations in the urine.
High levels of OXALATE
in the urine (called HYPEROXALURIA)can result from genetic defects and also from
diet. Certain oxalate containing foods such as chocolates
(dark or milk) and berries contain
large amounts of oxalate. People with moderate hyperoxaluria
and without genetic defects are encouraged to avoid high oxalate containing foods
and to eat foods containing calcium, such as dairy products.
These people usually have what is called Dietary
may be particularly beneficial to eat these calcium containing foods
with meals. Since calcium binds oxalates contained in the food,
it prevents the absorption of oxalate in the gut. The calcium-oxalate
complex in the gut is non-absorbable and will be passed in the stool. In
fact, stone formers on low calcium diets form more stones.
Another form of
hyperoxaluria is Enteric
with this condition usually have digestive disorders such as Crohn's disease, ulcerative colitis, chronic
pancreatitis, ileal bypass surgery for the treatment of obesity, or
celiac sprue. These conditions are are characterized by an
inability to absorb fat (fat malabsorption). which leads to excess
oxalate absorption. Treatment includes avoiding high oxalate
foods and calcium with meals to bind oxalate in the gut to prevent
A rare genetic
disease is Primary
Hyperoxaluria. This is
an inherited disease characterized by kidney stone
formation at a young age and very high urine oxalate levels.
It is due to a liver gene defect. The only effective treatment
is liver transplantation, so that affected people will receive a new
iver with the normal gene. Dieatary therapy is also encouraged
but likely of little or no benefit. If liver transplant is delayed, the kidneys
can be irreversibly damaged by massive crystal and stone deposition. If this happens, then a dual
kidney and liver transplantion may be needed. Another rare
cause of hyperoxaluria that must be considered is excessive
ingestion of vitamin c.
to low amounts of citrate in the urine. High citrate levels help
prevent stones from forming. Some causes include severe potassium deficiency,
high levels of protein in the diet, diarrhea, and metabolic acidosis
(including renal tubular acidosis). Treatment is usually with
potassium citrate. Monitoring the blood to detect excess potassium levels
may be necessary. Sodium citrate is avoided. Increased
sodium intake can cause increased calcium excretion in the urine and
contribute to hypertension in some patients.
to high urinary uric acid concentrations. Although this can
cause uric acid stones, it also can lead to calcium stones. It
is not fully understood how calcium stones occur. The uric acid crystal
may serve as a "seed" crystal on which calcium crystals
will grow, or uric acid may somehow cause calcium crystals to precipitate.
Dietary and pharmacologic treatments are available.