Kidney Stones - Causes

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Causes

Kidney stones develop as a result of a complicated interaction of biologic events that are most likely triggered by genetic susceptibility coupled with dietary factors. The process is not completely known.

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General Biologic Events Leading to Kidney Stones

The key process in the development of kidney stones is supersaturation.

This process involves salts that are carried in urine. Such salts may include calcium oxalate, uric acid, cystine, or xanthine.
These salts can become extremely concentrated under certain circumstances: if the volume of urine is significantly reduced; or if abnormally high amounts of crystal-forming salts are present.
When concentration levels reach the point at which the salts no longer dissolve, they precipitate out and form crystals.

Different factors may be involved in either reducing urine volume or increasing the levels of the salts.

Deficiencies in Protective Factors. Normally, urine contains protective factors that include magnesium, citrate, pyrophosphate, and various proteins and enzymes. These compounds may protect against stone formation in various ways:

Allowing salt in the urine to be at higher-than-normal concentrations without forming crystals
Preventing crystal formation
Coating the crystals and preventing them for adhering to the tube surface

Deficiencies in these protective substances, therefore, cause stones.

Changes in the Acidity of the Urine. Changes in the balance of acid to alkaline in the urine can affect stone precipitation.

Uric acid and cystine stones thrive in acidic urine.
Calcium phosphate and struvite stones thrive in alkaline.

Factors that Bind Crystals to the Kidney Tubules. Researchers are studying the cells lining the kidney tubules in order to understand how and why early crystals bind to the tubes long enough to form stones. Under investigation are elevated levels of substances that either cause crystals to adhere to the tubes or deficiencies in those that prevent them from sticking.

Causes of Calcium Stones

In general, calcium stones form when there are imbalances of components in the urine that either promote or inhibit formation of the stone. Often, the cause of calcium stones is not known, a condition called idiopathic nephrolithiasis. Increasingly, research suggests that abnormalities in metabolism (i.e., digestion and intestinal absorption of calcium or oxalate) are responsible for nearly all stones. Genetic factors may play a role in about half of these cases. A number of medical conditions and drugs can also affect digestion and intestinal absorption.