Why Are There Crystals In My Dog Or Cat’s Urine?

Ron Hines DVM PhD

To see what normal blood and urine values are, go here

For an explanation of causes of most abnormal blood and urine tests, go here

To see how tests are grouped, go here

Reason Why Crystals Might Be Observed Microscopically In Your Dog Or Cat’s Urine

Microscopic crystals in your pet’s urine often mean that the urine is very concentrated. Urine is often supersaturated (high specific gravity with lots of dissolved solids). Whether these solids begin to form small crystals depends on the temperature of the urine (crystals tend to form as urine cools), and various inhibitor and promoter substances present in the urine. What those substances are and how they work is poorly understood. (ref)

When those crystals are associated with urinary tract symptoms, they might be significant. When they are associated with struvite or oxalate urinary tract stones they always are. Most of these crystals can be identified by their shape and by the pH of the urine in which they were found. As I mentioned, common crystals that can be associated with urinary tract disease are struvite crystals (magnesium ammonium phosphate, triple phosphate) – associated with feline urological syndrome (FUS) and oxalate crystals (calcium oxalate mono or dihydrate). Some genetic metabolic defects can also cause crystals to be present in your pet’s urine (eg cystine crystals in male dogs or uric acid crystals in dalmatians).

Certain sulfa-containing antibiotics that pet are prescribed can also account for crystal formation in their urine. Sulfa and sulfur are not the same thing.

Remember that crystals found in stale urine or previously refrigerated urine may not have formed in your pet. Animal hospitals can be very busy places and sometimes too much time passes before the sample is examined under a microscope. Crystals seen in very concentrated first-of-the-morning urine or samples from dehydrated pets may not be a sign of disease nor of crystal formation throughout the day. The presence of other urine abnormalities and the pet’s symptoms should be the decision makers.

Complementary tests:

urine pH, Blood calcium levels, crystal specimens submitted to laboratory for identification.


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