Crystalluria in Cats

By Catherine Barnette, DVM

What is crystalluria?

Crystalluria refers to the presence of crystals in the urine. These crystals are made up of minerals and other substances that would normally be dissolved in the urine; crystals form when these substances do not remain dissolved in the urine and instead coalesce 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.

There are a variety of different types of urinary crystals that may be seen in cat urine, although the most common forms are calcium oxalate crystals and magnesium ammonium phosphate (struvite).

What causes crystalluria?

In some cases, crystalluria is simply an artifact of handling. As urine cools (for example, if a urine sample was refrigerated prior to analysis or left sitting at room temperature), substances that would normally remain dissolved can precipitate out of the urine and form crystals. If you have ever tried to mix a very sweet batch of sweet tea, you have probably observed that you can dissolve more sugar in hot tea than in cold tea; the same is true for various substances that are normally found dissolved in the urine. If crystalluria develops after the urine is out of the cat’s body, once the temperature has begun to cool, it is not medically significant or a cause for concern.

In other cases, however, crystalluria may be associated with a problem that makes your cat more likely to develop urinary stones. In these cats, the presence of crystals may indicate a high concentration of crystal-forming substances within the urine, abnormally concentrated urine, an unusually high or low urine pH, a diet that is high in certain substances, or the ingestion of certain toxins. Therefore, it’s important for your veterinarian to determine whether your cat’s crystalluria is clinically significant, in order to determine whether treatment is necessary.

What are the clinical signs of crystalluria?

Crystalluria by 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 within the urinary tract.

If crystalluria is accompanied by the presence of bladder stones or other urinary disease, such as feline idiopathic cystitis, you may see signs of lower urinary tract inflammation. Affected cats may strain to urine, urinate outside of the litter box, have blood in their urine, or frequently pass small volumes of urine.

How is crystalluria diagnosed?

Crystalluria is diagnosed via 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). Once a urine sample has been collected, it is centrifuged (spun at a high rate of speed). This allows any crystals, cells, and other debris in the urine to sink to the bottom of the test tube, where it 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.

Depending on the degree of crystalluria that is presence, as well as your cat’s clinical signs and any other abnormal urinalysis findings, your veterinarian may recommend additional testing to determine the significance of your cat’s crystalluria. Further diagnostics might include additional urine testing, to determine whether the crystals are a consistent finding and whether they are present even on a fresh urine sample. Your veterinarian may also recommend abdominal radiographs to rule out bladder stones. If crystals are rare and your veterinarian is relatively confident that they are merely an artifact, there may not be a need for further testing.

Will my cat require treatment for crystalluria?

Many cases of crystalluria are not clinically significant. If your veterinarian determines that this is the case for your cat, no treatment will be needed.

If your cat has clinically significant crystalluria, your veterinarian may recommend a number of 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. Through the use of running water fountains and/or flavored water (adding a small amount of low-sodium chicken broth or tuna juice to regular water), you can encourage your cat to drink more water and pass more dilute urine. These measures can help decrease the likelihood of your cat forming urinary stones and experiencing other negative impacts as a result of crystalluria.

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