Why Are There White Blood Cells 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

White Blood Cells In Your Pet’s Urine = WBCs, Leukocytes

A microscopic examination of your dog or cat’s urine for the presence of white blood cells is a standard part of its complete urinalysis – the examination of its urine. Vets like myself are happiest when very few or none are seen.

The number of white blood cells in your dog or cat’s urine is recorded as the number seen through a microscope using the high power lens (= number per high power field = #/HPF). Less than four or five is considered OK. When there are more, it is a sign of inflammation – usually a bacterial infection somewhere in the pet’s urinary tract (pyuria). The white blood cells seen are usually neutrophils. Often the bacteria that account for their presence can be seen as well. The number of white blood cells or leukocytes present can also be roughly estimated by the color change that appears in certain urine dipstick diagnostic strips. (ref) WBCs (leukocytes) contain esterase enzymes that turn a square portion of the urine dipsticks purple.

However the presence of increased numbers of WBCs, stimulated by the bacteria’s presence, rarely mean that bacteria are working alone to cause your pet’s problem. There is usually a deeper underlying cause for your pet’s urinary tract infection (UTI). The presence of stones (calculi formed of oxalate, struvite, etc), retention of urine due to neurological problems (eg spinal cord injuries), birth defects in the architecture of the urinary tract, tumors in the tract, etc. are often the real underlying causes. Confirmed in humans, immune system variability is another known cause. (ref) Urinary tract infections (UTIs) are also more common in female pets. That is because their urethra is shorter and wider than it is in males. UTIs are also considerably more common in pets that were spayed too young . Pediatric spays that are performed before your pet’s vagina has had time to fully assume its adult shape – leave the pet susceptible to bacterial invasion of the urinary system. (ref) That is particularly true if the pet is overweight as well.

White blood cells are more difficult to correctly identify in urine that has a pH greater than 7 (=alkaline). Alkaline urine is, in itself, worrisome in cats and dogs. White blood cells/leukocytes are also more likely to break up and become invisible (lyse) when your pet’s urine is very dilute or when the sample examined is stale. Your pet’s first urine of the morning is always the most informative to your veterinarian.

Bleach, used to rinse containers in which urine is collected, can cause false positive dipstick leukocyte/WBC reactions when the container has not fully dried and aired out before it is reused.

Complementary Tests:

Urine bacterial culture and antibiotic sensitivity of bacteria found in an aseptically-collected  urine sample. Diagnostic imaging when an anatomical defect in your pet’s urinary system is suspected or when repeat infections occur.


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