Crystalluria in Cats

What is crystalluria?

Crystalluria refers to the presence of crystals in the urine. These crystals are composed of minerals and other substances that normally would be dissolved in the urine, but instead join together into crystals. While crystalluria can be a medically significant condition, it can also be an incidental finding that has no medical relevance for the affected cat. Various types of urinary crystals may be seen in cat urine, but the most common types are calcium oxalate and magnesium ammonium phosphate (struvite).

What causes crystalluria?

In some cases, crystalluria occurs simply due to handling the urine. As urine cools, substances that normally remain dissolved can join together and form crystals (e.g., when a urine sample is refrigerated prior to analysis or left sitting at room temperature). You can dissolve substances more easily in a warm liquid than a cold liquid, as you may have noticed when stirring sugar into tea or coffee. The same is true for the substances normally found dissolved in the urine.

If crystalluria develops after the urine is out of the cat’s body and begins to cool, it may not be medically significant or a cause for concern. Unfortunately, in many cases, crystalluria is associated with a problem that makes your cat more likely to develop urinary stones. In these cats, the presence of crystals may indicate several things:

• A high concentration of crystal-forming substances within the urine
• Abnormally concentrated urine
• An unusually high or low urine pH
• A diet high in certain substances
• Ingestion of certain toxins

It is important for your veterinarian to determine whether your cat’s crystalluria is clinically significant to determine whether treatment is necessary.

What are the clinical signs of crystalluria?

Crystalluria itself is not associated with any clinical signs. Urinary crystals are microscopic and they do not cause any pain unless they combine to form larger stones in the urinary tract.

If crystalluria is accompanied by bladder stones or other urinary diseases, such as feline idiopathic cystitis (FIC; also called Pandora Syndrome), you may see signs of lower urinary tract inflammation. Affected cats may strain to urinate, urinate outside the litter box, have blood in their urine, or frequently pass small volumes of urine.

How is crystalluria diagnosed?

Crystalluria is diagnosed by urinalysis. Your veterinarian will first obtain a urine sample from your cat. This sample may be obtained from a litter box (using non-absorbent litter), via a urinary catheter (which is inserted into the urethra to collect urine from the bladder), or via cystocentesis (in which a long needle is passed through the abdominal wall directly into the bladder).

The urine sample is then centrifuged (spun at a high rate of speed), which allows crystals, cells, and other debris in the urine to sink to the bottom of the test tube where they can be isolated. This pellet of crystals, cells, and debris will then be dissolved in a very small amount of urine and viewed under a microscope. If crystals are seen on microscopic examination, your cat will be diagnosed with crystalluria.

Your veterinarian may recommend additional testing to determine the significance of your cat’s crystalluria, depending on the degree of crystalluria present as well as your cat’s clinical signs and any other abnormal urinalysis findings. Further diagnostics might include additional urine testing to determine whether the crystals are a consistent finding and whether they are present on a fresh urine sample.

Your veterinarian may also recommend abdominal radiographs (X-rays) or ultrasound to rule out bladder stones. If crystals are rare and your veterinarian is relatively confident that they are merely artifacts (abnormalities caused by the method testing and not an illness), further testing may not be needed.

Will my cat require treatment for crystalluria?

Many cases of crystalluria are not clinically significant. In these cases, no treatment is needed.

If your cat has clinically significant crystalluria, your veterinarian may recommend several interventions to help decrease crystal formation and decrease the likelihood of bladder stones. In some cases, a specific cause of crystalluria can be identified and that cause can be alleviated. In many cases, however, treatment focuses on long-term management to reduce crystal formation. Increasing water intake, regulating urine pH, and encouraging frequent urination can all play a role in decreasing crystalluria in affected cats.

Your veterinarian may recommend a prescription diet and/or medications to change the chemical composition of your cat’s urine and discourage crystal formation. Additionally, you may be advised to take steps to encourage your cat to drink more water by using running water fountains and/or flavored water (adding a small amount of low-sodium chicken broth or tuna juice to regular water). These measures can help decrease the likelihood of your cat forming urinary stones and experiencing other negative impacts because of crystalluria.