A bladder stone, or urolith, is comprised of minerals held together in an organic matrix. There are many different types of bladder stones -- they vary according to which minerals they contain. Of all the different kinds of bladder stones, though, struvite is the most commonly encountered in cats. In a certain urinary environment, the amount of struvite stone minerals present in the urine becomes so significantly high that they are unable to remain in the dissolved state. Instead, the magnesium and phosphorus minerals will precipitate, or fall out of solution, into crystals that in turn will conglomerate into stones. The incidence of the struvite stone has decreased in the last 10 or so years due to the development of preventive diets.
Among felines, calcium oxalate is the second most commonly diagnosed stone type. The mode of formation of these stones is not completely understood. It is believed that the struvite prevention diets are inadvisable for cats prone to forming calcium oxalate stones, since the magnesium restriction and urine acidification may influence calcium oxalate stone formation.
With all types of bladder stones, frequent urination, blood in the urine, and difficulty urinating may result. Irritation of the bladder generally is the cause of blood in the urine and frequent urination. When a stone obstructs the bladder outflow -- a much more threatening condition -- a severely decreased ability or inability to urinate results.
