Kidney Stones : Types

Kidney stones or renal stones are gravel-like collections of chemicals that may appear in any area of the urinary system, from the kidney to the bladder. They may be small or large, single or multiple.

Of the four main types of urinary stones, calcium stones are the most common.

(1) Almost 95% of all kidney stones are calcium stones. They occur when there is too much calcium in the urine. Defective kidney function may allow too much calcium in the urine, or excessive calcium may be absorbed from the stomach and intestines. Some calcium stones are caused by an excess of a chemical called oxalate, present in many foods, which binds easily with calcium to form a stone. The risk of calcium stone formation is increased if suffering from hyperparathyroidism and inflammatory bowel disease.

(2) A second type of kidney stone is made of uric acid. These stones are much less common than calcium stones. Uric acid stones occur because of too much uric acid in urine. They might occur in case of dehydration. Uric acid stones are common in people who have gout, a disease that causes high uric acid levels in the blood.

(3) A third type, struvite stones, is thought to be formed as a result of an interaction between protein-breakdown products and infection-causing bacteria in the urine.

(4) Finally, a rare type of kidney stone is a cystine stone. It occurs if one has the genetic disease called cystinuria. This disease results from a birth defect that causes the kidney to allow too much cystine into the urine. This type of stone formation is almost always diagnosed during childhood.

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