What Are Urine Crystals and Bladder Stones in Cats?
Bladder stones and crystals are solid waste particles that form in a cat’s urine.
Waste materials can be concentrated inside of the bladder, resulting in stones or crystals. This is especially common if a cat is dehydrated or eating primarily dry food.
These crystals can only be seen under a microscope, but over time they can get bigger, and eventually can become stones as big as the bladder itself.
Stones or crystals can be found in the kidneys in the tube that connects the kidney to the bladder (ureter), in the bladder itself, or in the tube that connects the bladder to the outside of the body (urethra).
What Is the Difference Between Urine Crystals and Bladder Stones in Cats?
Crystals are the building blocks of bladder stones.
There are different types of crystals and stones that can form depending on various factors, such as the acidity of the urine, the concentration of the urine, genetic factors, diet, and other conditions.
It's also possible to have a stone that is made up of more than one type.
Types of Urine Crystals and Stones in Cats
Struvite—Also called magnesium ammonium phosphate stones, struvite is one of the two most common stones in cats. This is due to a multitude of factors such as breed, sex, and diet.
Struvite crystals and stones are extremely common, especially in cats that eat primarily dry food. Magnesium ammonium phospahate causes these (commonly known as “ash” in pet foods).
Although the disease caused by this type of crystal is most severe in male cats, female cats can also be affected.
Sometimes these can be dissolved out with a prescription diet, but occasionally surgery is required. Often, they can be prevented by feeding a cat an exclusively canned food diet.
Calcium oxalate are another type of crystal and stone that are commonly seen in cats. These are much more stubborn than struvites, often requiring surgery.
After surgical removal, they can be controlled by feeding a prescription diet designed to control the amount of calcium and oxalate biproducts in the urine. Canned food is preferred to dry food.
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Symptoms of Urine Crystals and Bladder Stones in Cats
Symptoms of bladder cystals or stones in cats include:
Small, frequent urinations
Straining to urinate
“Accidents” outside of the litter box—especially places like sinks or laundry
Signs your male cat may be experiencing a urinary emergency:
Frequent trips to the litter box with little or no urine produced
Straining with little to no urine produced
While symptoms seen in bladder crystals and stones are similar, symptoms of bladder stones tend to go on longer than crystals.
Causes of Urine Crystals and Bladder Stones in Cats
There are several different reasons a cat may develop crystals and stones, including underlying health conditions, breed, and age.
However, in the vast majority of cases (particularly of the common struvite crystals/stones), a dry food diet plays a large role.
The underlying cause of calcium oxalate crystals/stones are less precise, but diet still plays a major part. Some cats don’t tolerate urine that is heavily saturated with calcium and/or oxalate as well, resulting in crystal formation. This is why long-term management involves specially designed (prescription only, there are no over-the-counter alternatives) diets which are meant to adjust the levels of waste products below levels that will form crystals.
How Veterinarians Diagnose Urine Crystals and Bladder Stones in Cats
Diagnosis of a stone, crystals, or a blockage includes the following diagnostic tests performed by your vet:
Bloodwork—To look for underlying conditions that may cause certain crystals or stones, or to evaluate the presence/severity of a blockage
Urinalysis—To evaluate the urine environment including the concentration of the urine, the acidity or non-acidity of the urine, and the presence of infection or crystals
Imaging—This includes X-rays or ultrasound to visually look for stones
Treatment of Urine Crystals and Bladder Stones in Cats
Treatment of crystals/stones depends on the type of crystal/stone, the size and location of the stone, and your cat’s history.
Female cats are often able to pass small stones, either on their own or with a flushing procedure called voiding urohydropropulsion.
Male cats, however, are at higher risk for a urinary blockage, even with very small stones. Their urethra is constricted because the stone/crystal needs to travel through their penis. This forms a bottleneck where the stones/crystal become jammed up and causes an obstruction.
Some stones are dissolvable within two-to-four weeks of starting a prescription diet. However, larger stones can dissolve to a small enough size that they can also cause a urinary blockage. Stones must be removed surgically if they are too big and not able to dissolve. Most calcium oxalate stones will not be dissolved by prescription diet and require surgical removal.
A urinary blockage typically requires several days of hospitalization to stabilize your cat, and one-to-two weeks for a full recovery. If a stone is blocking the flow of urine, your vet will insert a catheter to flush the stone back to the bladder. Then, the stone must either be dissolved or surgically removed to prevent another blockage.
Recovery and Management of Urine Crystals and Bladder Stones in Cats
Your cat’s recovery from urine crystals and bladder stones depends on the type of stone and your cat’s health history.
Diet is the most common management strategy since there are several commercial diets designed to treat and/or prevent the most common types of crystals/stones. Increasing water intake is another strategy, as crystal/stone formation is more likely in concentrated urine. Feeding canned food is an efficient way to also increase water intake.
Prevention of Urine Crystals and Bladder Stones in Cats
It’s important to realize that crystals and stones in cat urine can recur.
First, if your cat has already had crystals/stones, increase their water intake, and feed them the specific diet recommended by your veterinarian. Do not feed them any other foods—discuss any changes to your cat’s diet with your veterinarian first.
Diluting your cat’s prescription food with other diets, treats, or snacks can lead to a recurrence of the problem. These foods are carefully adjusted to provide exactly the right urine concentration to prevent crystals/stones.
A recheck urinalysis will also help you to know if a problem is developing before symptoms start. Be sure the sample is fresh, as struvite crystals can develop in older urine that’s been left out.
If your cat has not had an issue, feeding an all-canned quality diet is the best way to help prevent formation of urine crystals and bladder stones. Encourage your cat to drink a lot of water by using water fountains, running water, or flavor their water with a little bit of tuna juice.
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