FELINE STRUVITE BLADDER STONES
STRUVITE BLADDER STONES IN THE CAT
WHAT IS STRUVITE?
Struvite is a urinary mineral composed of ammonium, phosphate, and magnesium. These three substances are common in urine and if they exist in high enough concentrations, they will bind together in the form of crystals. Struvite crystals are found in urine normally and have no significance on their own. Problems occur when these crystals combine with mucus and form a urinary plug that can actually cause a blockage in a male cat’s urinary tract (see our page on Feline Urinary Blockage) or when the crystals bind together to form an actual bladder stone.
Struvite is also sometimes called “triple phosphate,” based on some early studies that had misidentified the minerals. The name has stuck, though, so you may hear this term.
In older times, feline bladder stones could virtually be counted on to be struvite, as opposed to some other type of mineral. Nowadays, because of widespread cat food reformulation in the 1980’s approximately 50% of feline bladder stones are struvite and the other 50% are calcium oxalate.
IF STRUVITE CRYSTALS ARE NORMAL, WHY DO SOME CATS FORM STONES?
While bladder stones can sometimes be found incidentally while looking into another problem, most of the time they are found when the cat is showing signs of lower urinary tract disease:
TREATMENT: DIETARY DISSOLUTION
Struvite stones can be dissolved by feeding special diets. There are several commercial brands available and they all act by creating a bladder environment that is favorable to dissolving the struvite crystals back into the urine. In order to proceed with this form of treatment, the patient should be female (as the stone dissolves and the stone gets smaller, we do not want it lodging in the narrow male urinary tract and causing obstruction). Obviously, the cat should not have a second disease which makes the stone diet inappropriate and the cat must be fed only the urinary diet and nothing else.
Surgery to remove a bladder stone is called a “cystotomy.” Here, the bladder is opened and the stones inside are simply removed. The bladder and belly are closed up and the cat is able to go home when he or she has a good appetite and normal urination. Some blood in the urine can be expected for several days after surgery and there may be some urinary discomfort at first but generally removing the stones is the fastest route to recovery from urinary symptoms.
The stones can be sent to a special laboratory for analysis to confirm the stone type.
OTHER METHODS OF STONE RETRIEVAL
To avoid forming new struvite stones it is helpful to use a diet that creates a bladder environment that is not conducive to stone formation. There are numerous such urinary formulas and sometimes the same diet that was used to dissolve the stone can simply be continued. Ideally, a canned formula is used as canned foods have extra water and the extra water helps make for a more dilute urine (and a dilute urine means a lower crystal concentration).
If it is not possible to feed an appropriate diet, the use of urinary acidifiers may be necessary. Your veterinarian may recommend some monitoring tests to make sure the pH and urine concentration stay in a range where struvite stones should not form.
Page posted: 10/25/11