Struvite Bladder Stones in Cats

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

What are struvite bladder stones?

Struvite bladder stones are one of the most common bladder stones in cats. These stones are composed of a mineral called struvite, which is a combination of ammonium, phosphate, and magnesium.

Struvite and struvite crystals are a normal finding in urine, at low levels. In some pets, however, these struvite crystals come together to form an actual stone within the urinary tract. These stones can irritate the urinary tract and have the potential to cause a urinary obstruction (blockage).

What causes struvite bladder stones?

In some cats, struvite bladder stones form because of a urinary tract infection. Certain species of urinary bacteria produce a chemical called urease, which leads to changes in urine acidity. Urease-producing bacteria can contribute to the formation of struvite stones.

In most cases, however, cats develop struvite stones in the absence of an infection. In these cases, the exact cause is unknown. Several different factors have been found to contribute to these stones, including the formation of concentrated urine, increased urine pH (alkaline urine), and increased levels of magnesium and phosphorus within the urine.

Struvite stones have been shown to be more common in female cats than males. There is also evidence to suggest that genetic factors may play a role in their development, but no specific breed predisposition has been found.

What are the signs of struvite bladder stones?

Struvite stones, like other bladder stones, cause significant inflammation and irritation of the bladder wall. Therefore, they cause signs similar to those of a urinary tract infection or other inflammatory bladder disease.

"A complete obstruction is potentially life threatening and requires immediate emergency treatment."

Signs of bladder stones typically include frequent urination, straining to urinate, blood in the urine, and urinating outside of the litterbox. Some cats show non-specific signs of discomfort, such as tiredness and decreased appetite. In some cats, bladder stones produce no symptoms at all. These stones may be detected as part of the workup of another condition.

Large stones may act almost like a ball valve, causing an intermittent or partial obstruction at the neck of the bladder, where the bladder attaches to the urethra. Small stones may flow with the urine into the urethra where they can become lodged and cause an obstruction. If an obstruction occurs, the bladder cannot be emptied fully; if the obstruction is complete, the cat will be unable to urinate at all. If the obstruction is not relieved, the bladder may rupture. A complete obstruction is potentially life threatening and requires immediate emergency treatment.

How will my veterinarian diagnose struvite bladder stones?

If your cat is having urinary issues, your veterinarian will first recommend a urinalysis, in which a small urine sample is sent for chemical analysis and microscopic examination. Struvite stones are most often seen in concentrated urine that has an increased pH. On microscopic examination, your veterinarian will likely see red blood cells (caused by irritation of the bladder wall), white blood cells (consistent with inflammation), and increased numbers of struvite crystals.

Your veterinarian may also recommend blood tests, including a complete blood cell count and serum biochemistry profile. These tests assess your cat’s overall health and rule out other medical conditions that may be contributing to your cat’s urinary signs.

"On X-rays, struvite stones typically look like smooth rocks or pebbles within the bladder."

Finally, your veterinarian will likely recommend abdominal X-rays (radiographs). X-rays are the most effective way to diagnose bladder stones because most (including struvite) are visible on radiographs. On X-rays, struvite stones typically look like smooth rocks or pebbles within the bladder. Ultrasound may also be used to visualize bladder stones.

How are struvite bladder stones treated?

There are two basic categories of treatment for struvite bladder stones: medical dissolution and surgical removal.

Medical dissolution (dissolving) is accomplished by feeding a specially formulated prescription diet. These diets are intended to alter the pH and chemical composition of the urine in a way that causes the stone to gradually dissolve. For dissolution to be effective, the cat must eat only the prescription food; no treats or other food can be given. X-rays are repeated every few weeks during this process, to monitor progress and ensure that the stones are shrinking in response to the diet. Most struvite stones dissolve within one to two months. f a urinary tract infection was diagnosed at the same time as struvite stones were found, antibiotic therapy will also be required while the diet has a chance to work.

Some cats are unable to eat a prescription diet, due to either a medical condition or factors in the home. In these cats, bladder stones can be surgically removed in a procedure called a cystotomy. A cystotomy is performed under general anesthesia. Your veterinarian will first make an incision into your cat’s abdomen and then make an incision into the bladder to remove the stones. Once removed, the stones are sent to a laboratory to confirm their chemical composition. Recovery from a cystotomy typically takes one to two weeks. During this time, cats must have their activity restricted to allow their incision to heal. Some abdominal pain and blood in the urine are normal for the first several days after a cystotomy.

Less commonly, bladder stones are removed via a process known as cystoscopy. This involves inserting a small camera into the bladder, along with a basket or other retrieval device that can be used to remove the stones. Alternative techniques have been described to remove bladder stones, but these techniques are less commonly used and are only practical for very small stones.

Will struvite bladder stones recur after treatment?

Cats who have developed struvite bladder stones are likely to experience a recurrence later in life, unless the conditions that led to the formation of stones can be corrected.

The most important step to preventing recurrence is to feed a prescription diet. These diets are specially formulated to create a urine environment that is less favorable for the formation of struvite bladder stones. In general, these diets decrease the urine pH and restrict the levels of magnesium, ammonium, and phosphorus in the urine.

Additionally, you will need to increase your cat’s water intake to make your cat’s urine less concentrated. In most cases, using the canned version of your cat’s prescription diet will keep the urine dilute. In some cases, you may need to take additional steps, such as using a cat water fountain, offering flavored water (a small amount of chicken broth or tuna juice can be used), or adding additional water to canned food.

Your cat will require long-term, regular re-checks. This will allow your veterinarian to monitor your cat’s urine in order to ensure that her urine characteristics remain within desired parameters. Regular monitoring will also allow future recurrence of bladder stones to be detected early, when treatment may be easier and more effective.

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