Kidney stones are one of the most common and painful kidney disorders. About 10% of men and 3% of women will develop a kidney stone at some point in their lives. For many, stones becomes a chronic problem, since people who get one stone are more likely to develop others.
The kidneys, each about the size of a fist, are located in the lower back. They are connected to the bladder by narrow tubes called ureters. The kidneys act as filters for the bloodstream, catching needed substances and returning them to circulation, and disposing of unneeded substances in urine. Urine collects in the bladder and then passes through another narrow tube called the urethra and out of the body.
Kidney stones are formed when minerals and other substances accumulate in the kidneys and become so concentrated that they crystallize into solid particles. Under normal circumstances, urine contains chemicals that keep this from happening, but under certain conditions this mechanism can fail. If the resulting crystallized particles remain small, they can pass through the urinary system without any problems. Larger stones, though, can become lodged in the kidney or at any point further down the urinary tract.
There are five main types of kidney stones:
Calcium oxalate and calcium phosphate stones — These two types are the most common, accounting for about 80% of cases. These kidney stones usually form when the concentration of calcium or other minerals in the urine becomes too high, which in turn leads to formation of crystals and with time small, hard, rigid-formed masses. The exact cause of kidney stone is unknown in approximately 50% of cases. Possible causes include:
Struvite stones — These types of stones are composed of ammonium, magnesium, and phosphate salts. These develop as the result of a urinary tract infection and are usually seen in women.Patients with spinal cord injuries or other problems with the bladder are at a higher risk for forming this type of stone.
Uric acid stones — May develop in people who have gout, a condition that occurs when uric acid— a byproduct of protein metabolism— accumulates in the body. They are also seen in people undergoing chemotherapy. Preventive measures include a purine diet and medications such as allopurinol.
Cystine stones — Due to a rare genetic disorder that causes the kidneys to accumulate excess amounts of cystine, one of the amino acids that make up proteins.
Harrison's Principles of Internal Medicine. 15th ed. McGraw-Hill; 2001.
National Institute of Diabetes and Digestive and Kidney Diseases website. Available at: http://www2.niddk.nih.gov/.
National Kidney Foundation website. Available at: http://www.kidney.org/.
Coe FL, Evan A, Worcester, E. Kidney stone disease. J Clin Invest. 2005;115:2598-2608.
Edits to original content made by Western New York Urology Associates.
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