A kidney stone is a hard mass of crystals that have separated out from the urine. According to the National Institute for Diabetes and Digestive and Kidney Disease, kidney stones account for almost three million doctor visits and more than half a million emergency room visits per year in the United States. Although kidney stones occur most often in men over 40, reports the Mayo Clinic, stones can occur at any age and in either gender. Risk factors include dehydration; obesity, and eating foods high in protein, sodium or sugar; and family history. Symptoms may include sudden pain in the back or side, blood in the urine, nausea and vomiting.
There are different types of kidney stones, and the exact cause depends on the type of stone.
Calcium Stones
Calcium stones, the most common type of kidney stones, occur more often in men than in women. According to the University of Maryland Medical Center, an excess of calcium or oxalate in the urine causes many calcium stones. Medical conditions, including an overactive parathyroid gland, short bowel syndrome and severe vitamin B6 deficiency, can contribute to calcium stone formation. Genetic factors may play a role in about half of these cases.
Uric Acid Stones
Uric acid forms when the body breaks down purines---chemicals found in human body issues and in some foods, including meats and dried beans. According to the University of Maryland Medical Center, a number of conditions and other factors---gout, type 2 diabetes, chronic diarrhea, binge drinking, eating too much protein---may cause or contribute to uric acid stones. Certain medications, including chemotherapy, diuretics, allopurinol and salicylates, can also contribute to the formation of uric acid stones.
Struvite Stones
According to the National Institutes of Health, struvite stones are most common in women with urinary tract infections. Bacteria produce certain enzymes that raise the concentration of ammonia in the urine, causing stones that can become so large that they block the kidney, ureter or bladder.
Cystine Stones
Cystine is a component of muscles, nerves and other parts of the body. When it builds up in the body, cystine stones can form. The University of Maryland Medical Center reports that cystine stones are rare, and the disorder causing them runs in families. Other stones, including cystine and xanthine stones, are usually due to genetic abnormalities.
Xanthine Stones
According to the Merck Manual, xanthine stones can form when an inherited metabolism disorder causes a deficiency in the level of an enzyme that is used to break down uric acid. When excess xanthine precipitates in the urine, the resulting stones can cause pain and blood in the urine. Patients being treated with allopurinol for gout may also develop xanthine stones.
References
- National Institutes of Health: Kidney Stones
- University of Maryland Medical Center:Urological Disorders - Kidney Stones
- Mayo Clinic: Kidney Stones--Causes
- National Institute of Diabetes and Digestive and Kidney Diseases: Kidney Stones in Adults Diseases: Bariatric Surgery for Obesity
- Merck Manual: Inherited Disorders of Purine and Pyrimidine Metabolism Disorders
