The kidneys are 2 fist-sized organs that sit on each side of the spine. They are connected to the bladder by narrow tubes called ureters. The kidneys filter the blood. They catch needed substances, such as salt and water, and return them to blood. They also pass wastes in the urine. Urine is stored in the bladder until it is ready to be eliminated from the body. Urine is passed out of the body through a tube called the urethra.
Kidney stones form when minerals and other matter buildup in the kidneys. Over time, they crystallize into solids. Normally, contents of the urine can keep this from happening. The solids remain small and are flushed out with the urine without any problems. Some stones do not pass through, but get bigger. Larger stones cause problems when they get lodged in the urinary tract.
Kidney stones are one of the most common (about 1 in 10 people will have them) and painful kidney problems.
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Kidney stones are made from:
- Calcium oxalate and calcium phosphate—The most common types, making up about 8 of 10 kidney stones. These are mainly formed when calcium or other minerals becomes too high in the blood.
- Struvite—Made up of a mix of mineral salts. They are caused by urinary tract infections.
- Uric acid—Formed when the uric acid level becomes high. They may also happen in people with gout or those having chemotherapy.
- Cystine—Caused by a rare problem with genes that results in a buildup of cystine in the kidneys.
Definition & facts for kidney stones. National Institute of Diabetes and Digestive and Kidney Diseases website. Available at: https://www.niddk.nih.gov/health-information/urologic-diseases/kidney-stones/definition-facts. Updated May 2017. Accessed April 2, 2019.
Kidney stones. National Kidney Foundation website. Available at: https://www.kidney.org/atoz/content/kidneystones. Accessed April 2, 2019.
Kidney stones. Urology Care Foundation website. Available at: https://www.urologyhealth.org/urologic-conditions/kidney-stones. Accessed April 2, 2019.
Nephrolithiasis in adults. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T114904/Nephrolithiasis-in-adults. Updated March 22, 2019. Accessed April 2, 2019.
Urinary calculi. Merck Manual Professional Version website. Available at: https://www.merckmanuals.com/professional/genitourinary-disorders/urinary-calculi/urinary-calculi. Updated March 2018. Accessed April 2, 2019.
Last reviewed March 2019 by EBSCO Medical Review Board Adrienne Carmack, MD Last Updated: 4/2/2019