Kidney Stones

Also known as renal calculi, form when substances in the urine concentrate and coalesce into hard, solid lumps in the kidney. Calcium-containing stones are the most common, accounting for about 70 to 80 percent of renal calculi (most of these consist of calcium oxalate or calcium phosphate). Other stones are composed of uric acid or a combination of magnesium, ammonium, and phosphate.