Kidney stones form in the urinary tract from substances naturally found in the urine such as calcium, magnesium or uric acid. Kidney stones vary in size, shape and color and are generally of three types: calcium, struvite or uric acid. Treatment of kidney stones varies depending on stone type. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) stresses the importance of distinguishing stone types to determine the proper course of treatment and measures to prevent recurrence.
Calcium Oxalate and Calcium Phosphate Stones
The majority of kidney stones are formed from high levels of calcium in the urine which can combine with oxalate and phosphate. Calcium, oxalate and phosphate are normal components of a healthy diet and normally processed and excreted through the action of the kidneys. Over time, however, calcium may combine with other metabolic waste products to form solid kidney stones. It is recommended by the NIDDK that individuals prone to kidney stones drink 12 glasses of water per day to help flush out excess calcium in the kidneys. Calcium kidney stones are most commonly formed from calcium oxalate with a minor calcium phosphate component. High dietary levels of oxalate may promote kidney stone formation; it is recommended that those at risk for kidney stones avoid high oxalate foods such as rhubarb, spinach, beets, chocolate and certain berries. Calcium phosphate stones lacking oxalate are very rare but can occur in individuals with acidic urine.
Struvite or "Infection" Kidney Stones
Struvite stones are more rare than calcium stones, representing about 10 percent of kidney stone cases. Struvite stones are also known as "infection stones," as they form through the action of bacteria in the urinary tract during a urinary tract infection (UTI). A review of kidney stones in the British Medical Journal describes how bacteria increase the alkalinity of urine to promote the precipitation of magnesium which form struvite stones. Struvite stones are commonly treated in conjunction with a course of antibiotics to fight the UTI, which can be a very serious medical condition.
Uric Acid Kidney Stones
Uric acid kidney stones form as a result of too much acid in the urine. They are less common than calcium stones, accounting for 10 percent of the incidence of kidney stones. A 2005 review of kidney stone disease in The Journal of Clinical Investigation explains that such stones are more likely to occur in obese and diabetic individuals, because of insulin resistance which leads to increased acid levels in the urine. Uric acid stones are less dense than calcium stones and therefore not easily seen by x-ray. If such a stone is found after passing through the urinary system, it may have a red or orange color. If uric acid stones recur, they may be treated with agents that help to increase the pH of urine.
