Why Does My Dog Or Cat's Urine Contain Oxalate Crystals ?













Ron Hines DVM PhD

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


To see how tests are grouped, go here

Oxalate Crystals Seen In Your Pet’s Urine

Most of the oxalate in your pet’s body is produced by normal processes in its liver and red blood cells. Oxalate (C2O42- ) is a normal end product of metabolism. If it has other functions in your pet’s body, we do not know what they are.

Your pet can also absorb oxalate (salts) from its diet. However, only plant ingredients are likely to contain significant amounts. Once produced, oxalate usually combines with free calcium in your dog or cat ’s blood stream. It normally leave your pet’s body in solution in its urine. But oxalate can form insoluble crystals combined with calcium in your pet’s urinary tract when the pet’s urine is acidic (pH under 7).

For most of the 20th Century, dog and cat diets were formulated to produce acidic urines to slow the formation of struvite crystals, the major cause of bladder and kidney stones in pets. However, the situation has now reversed; oxalate stones are now the most common in pets. So veterinarians can become concerned if oxalate crystals are seen in large numbers in your pet’s urine – particularly since vets have no way to dissolve large obstructive oxalate crystal stones once they have formed.


Reasons Why Oxalate Crystals Might Be Seen In Your Pet’s Urine :

A few oxalate crystals seen in your pet’s urine are not of concern unless your pet is experiencing urinary tract problems. Those problems always include pain and urgency. When that is not the case, a few oxalate crystals are irrelevant. They are more common to see when urine was not examined microscopically as soon as it was collected.

It may seem strange to you that something like oxalate crystals could sometimes be important and sometimes be unimportant. Perhaps if veterinarians better understood why stones form in one pet and not in another I could explain that better.

However, miniature schnauzers are particularly susceptible to to both oxalate crystals and urinary tract stones (for unknown reasons).

Disease of the parathyroid gland (hyperparathyroidism) causing high blood calcium levels might also increase urine oxalate levels and, perhaps stone formation.

Dangerous oxalate crystals also form in the kidney filters (glomeruli) after antifreeze poisoning and, rarely, in forms of cancer that elevate blood calcium level (eg lymphoma).

Whenever crystals of any kind are seen in your pet's urine the first thing that should come to mind is that the pet is not consuming sufficient water.

Complementary Tests :

Urinalysis, CBC/WBC and blood chemistry panel (including evidence of elevated blood calcium level), if accompanied by urinary tract distress or other abnormal urine parameters (tests) – the pet needs a diagnostic work-up (x-rays) for potential urinary tract stones (calculi), review of its diet and review of adequacy of its fluid intake.