Kidney stones stem from an accumulation of calcium, magnesium, uric acid and other substances naturally found in the excretory system. They occur in the kidneys and urinary tract and may vary in size, shape, density, texture and color, depending on their type and underlying cause. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) describes four major types of kidney stones: calcium, struvite, uric acid and cystine stones. It is medically important to distinguish between the types to ensure that a stone is properly treated and to prevent future occurrences.
Calcium Stones
About 80 percent of all kidney stones result from a combination of high levels of calcium in the urine together with oxalate and phosphate. While calcium, oxalate and phosphate are all normally found in the urinary system, they may build up solid deposits in the kidneys over time and break off to release a stone into the urinary tract. People with a previous personal or family history of kidney stones are most at risk for developing this type. The NIDDK recommends that people prone to kidney stones drink 12 glasses of water per day to help flush out excess calcium. High dietary levels of oxalate may also contribute to kidney stone formation. Those at risk for calcium kidney stones should also avoid oxalate-containing foods such as spinach, chocolate, rhubarb and beets.
Struvite Stones
Struvite stones are primarily made up of magnesium and ammonia. These stones represent about 10 percent of kidney stone cases. A review titled "Kidney Stones," published June 2004 in "The British Medical Journal" by Dr. Malvinder S. Parmar, explains that struvite stones are made through the action of bacteria in the urinary tract during an infection. For this reason, struvite stones are almost always associated with a urinary tract infection (UTI) and are referred to as "infection stones." Struvite stones and UTIs are treated with antibiotics. If left unchecked, UTIs can lead to serious medical complications in the kidneys and neighboring organs.
Uric Acid Stones
Uric acid kidney stones are less common than calcium stones and represent about 9 percent of kidney stones. A review titled "Kidney Stones Diseases," by Fredric L. Coe and a research team and published October 2005 in "The Journal of Clinical Investigation," explains that these stones form in people with acidic urine. Urine acidity is especially high in the obese and in diabetics as a result of insulin resistance. Uric acid stones tend to be less dense than calcium stones, and X-rays do not easily detect them. Such stones tend to accumulate orange-colored byproducts of the urinary system and may be red or orange in color. People at risk for uric acid stones are treated with drugs that increase urinary pH. The drugs help lower urine acidity and hinder stone formation.
Cystine Stones
Cystine stones form from an accumulation of the amino acid cystine in the urine. The incidence of cystine stones is very low, or 1 percent. The review of kidney stone diseases in "The Journal of Clinical Investigation," however, explains that cystine stones have a very strong genetic component. People with a family history of such stones are very likely to inherit genetic defects that promote their formation. While many pharmacological agents can treat cystine stones, those at risk should avoid cystine-rich foods (high-protein foods such as meats or nuts) and drink plenty of water to prevent stone formation.
