Kidney stones may develop in the kidneys or in the urinary tract if crystals of calcium phosphate or calcium oxalate that have separated out from urine grow too large to pass out of the body.
Illustration by Frank Forney. © 2016 Cengage Learning®.
Kidney stones are composed of crystals formed by chemicals that separate from the urine, harden, and build up in the kidney. Most people pass kidney stones out of the body without requiring medical treatment, but in severe cases, they might need surgery.
The kidneys are bean-shaped organs about the size of a juice box that are located on either side of the spine toward the back of the abdomen above the waist. They filter water, salts, and waste products out of the blood to make urine, and they maintain the body's water and ion * levels. When the ratio of water and ions in the urine is out of balance, kidney stones can form.
Kidney stones can be as small as a grain of sand or as big as a golf ball. There are four kinds of kidney stones:
The causes of kidney stones are often unknown. However, urinary tract infections, several metabolic disorders, and a family history of kidney stones may make a person more likely to develop them. People who have certain other conditions or genetic disorders may also develop kidney stones. These problems include the following:
The smallest kidney stones can pass out of the body in the urine without the person even knowing it. The passing of larger stones can cause severe pain, and people have described it as the worst pain they have ever experienced. The pain occurs when the stone moves from the kidney through the ureter *
Doctors can typically diagnose kidney stones based on the patient's medical and family history and a physical examination. In some cases, a doctor may also use x-rays and sonograms * , along with analyses of blood and urine to make the diagnosis.
Most kidney stones pass through the urinary tract on their own, and individuals typically help the process by drinking lots of water and taking pain medication. If the stones are very large (more than 0.5 inches, or 1.27 centimeters, in diameter), doctors can use various techniques to break up the stones while they are inside the kidney or ureter so that the smaller pieces can pass out without further medical intervention. One technique is extracorporeal shockwave lithotripsy (LITH-o-TRIPsee), which uses high-energy sound waves. These shock waves pass harmlessly through the body and break the stone into tiny particles, which the patient can then eliminate in the urine without pain. Surgery (nephrolithotomy) is rarely necessary.
Kidney stones usually affect people between the ages of 20 and 40. Approximately 10 percent of people experience kidney stones, and once a person has had one kidney stone, he or she has about a 70 to 80 percent chance of developing another. Once a person has passed a stone, a doctor tries to find out what kind it is, often by asking patient who has passed a stone at home to bring it in for laboratory analysis. This information may help the doctor determine why the person is developing the stones. In many cases, individuals can reduce their chances of developing more stones by changing their diet, drinking more water, and/or taking certain kinds of medication. Scientists have explored how certain urinary proteins are involved in stone formation. Their research as of 2015 showed that some proteins can keep the stone-associated chemicals from crystallizing out of urine and, therefore, prevent stone formation.
See also Gout • Kidney Disease • Metabolic Disease
Reinberg, Steven. “Kidney Stones Tied to Raised Heart Disease Risk in Women.” U.S. News & World Report, July 23, 2013. Available at: http://health.usnews.com/health-news/news/articles/2013/07/23/kidney-stones-tied-to-raised-heart-disease-risk-in-women (accessed April 6, 2016).
MedlinePlus. “Kidney Stones.” U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/kidneystones.html (accessed April 6, 2016).
National Institute of Diabetes and Digestive and Kidney Diseases. “What I Need to Know about Kidney Stones.” http://kidney.niddk.nih.gov/kudiseases/pubs/stones_ez (accessed April 6, 2016).
National Institute of Diabetes and Digestive and Kidney Diseases. 9000 Rockville Pike, Bethesda, MD 20892-2560. Telephone: 301-496-3583. Website: http://www.niddk.nih.gov (accessed April 6, 2016).
National Kidney Disease Education Program. 3 Kidney Information Way, Bethesda, MD 20892. Toll-free: 800-891-5390. Website: http://nkdep.nih.gov (accessed April 6, 2016).
National Kidney Foundation. 30 East Thirty-Third St., New York, NY 10016. Toll-free: 800-622-9010. Website: http://www.kidney.org (accessed April 6, 2016).
* ions are positively or negatively charged elements or compounds, such as hydrogen, sodium, potassium, and phosphate, which are necessary for cellular metabolism.
* ureters (YOOR-eh-ters) are tubelike structures that carry urine from the kidneys to the bladder.
* sonograms (SON-o-gramz) are images or records made on a computer using sound waves passing through the body.