Kidney stones are hard masses that form in the kidneys when there is not enough liquid to dilute waste chemicals in the urine.
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Kidney stones form when substances normally found in urine — such as calcium oxalate, uric acid, cystine or xanthine — lump together and become solid material within the kidneys. They may remain inside the kidneys or pass through the urinary tract, causing pain in the lower back and abdomen, as well as pain and bleeding during urination.
There is no single cause of kidney stones (also called renal lithiasis), but a range of medical conditions — as well as certain medications — may contribute to the formation of kidney stones.
Some conditions lead to an excess of chemicals in the urine or bloodstream. When these chemicals cannot be fully absorbed by the fluid present in urine (a state known as supersaturation), they may crystalize and form stones. And any condition or medication that reduces the amount of fluid in urine can also lead to supersaturation, and thus the formation of kidney stones.
To determine why a patient might be suffering from kidney stones, doctors will often examine the composition of the stones themselves once they pass through the body. This helps doctors determine what underlying medical issue might be causing the stones to develop.
Depending on a patient's underlying condition, a doctor might recommend that individuals avoid eating foods that can promote the development of kidney stones, such as foods high in protein or those high in oxalate, such as spinach, sweet potatoes, celery and green beans.
For some sufferers of kidney stones, the underlying cause may be genetic. Hypercalciuria, a condition that results in an overabundance of calcium in the urine, runs in families and is the most common condition afflicting those who suffer from calcium stones. Those with hereditary cystic kidney diseases are also at higher risk of developing kidney stones.
Non-hereditary conditions can also increase the risk of kidney stones. Hyperparathyroidism, a condition in which the parathyroid glands over-produce hormones, results in an excess of calcium in the bloodstream and has been known to lead to the formation of calcium stones in the kidneys.
Other disorders that can make individuals more susceptible to developing kidney stones include renal tubular acidosis, cystinuria, hyperoxaluria, hyperuricosuria, gout and chronic inflammation of the bowels.