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Your Dog 's White Blood Cell Count

Your Cat 's White Blood Cell Count

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

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

To see how tests are often grouped, go here

Ron Hines DVM PhD

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White Blood Cell Count

WBC, also part of your pet's CBC

Leukocyte Count, Leukogram

The job of your dog or cat ’s white blood cells is to defend its body. These cells (leukocytes) are the foot soldiers of its immune system. They appear white (white=leuko) when they form a layer in a centrifuged sample of your pet’s blood – hence their name.

When there are not enough of them (leukopenia) your pet is at risk of infection. When there are too many of them (leukocytosis) your pet is in an active battle against some perceived or imaginary foreign invader.

There are five basic types of white blood cells: neutrophils, eosinophils, basophils, lymphocytes and monocytes. Each has a different job - read about them through their name links.

All WBCs, except the lymphocytes originate in your dog or cat ’s bone marrow. All take their names from their appearance when observed on a stained microscope slide.

When your veterinarian orders a white blood cell count, it is generally along with a blood chemistry panel. When it is, it often includes a red blood cell count. In that case it is referred to a a CBC (complete blood cell count).

The report your veterinarian receives will give your pet’s white blood cell total numbers (in number of WBCs/microliter [ µL] of blood = Cells x 10 3 /cubic mm of blood = /µL).

It will also give the total number of each of the five cell types (=the absolute count) as well as the percentage of the total that each cell type made up (the differential count). All of those things help your veterinarian make sense of the data and can give important clues as to your pet's illness.

Reasons Why Your Pet’s White Blood Cell Count Could Be High (leukocytosis) :

Any form of inflammation, infection or tissue destruction that releases signaling chemicals (inflammatory cytokines, granulocyte colony-stimulating factor, C-reactive protein. etc.) into your pet’s blood stream will cause high white blood cell counts if your pet’s bone marrow is healthy.

Some forms of cancer also have this effect.
Generally, the more severe an infection or underlying disease is, the higher the WBC count will initially be.

Toxins that accumulate in organ failure (like kidney or liver disease) can also increase your pet’s white blood cell count. So can toxic products that your pet consumes (although that is usually secondary to tissue damaged caused elsewhere).

A very common problem when pets come to animal hospitals is their fear, apprehension and excitement; although some have those feeling much more than others

Being in that agitated, stressed state, releases two compounds that will increase your pet’s WBC count. Both are released by your pet’s adrenal glands. The first is epinephrine (adrenaline) that chemical increases your pet's heart and respiratory rate and dilates its pupils (the adrenaline rush). Another effect of epinephrine is an increased WBC count (leukocytosis) as white blood cells that once clung to the walls of blood vessels (the marginal pool) detach and move into circulation while additional WBCs stored in your dog or cat’s spleen are squeezed out into its blood stream. This happens fast – within minutes. In dogs, it is usually the more mature neutrophils (segs) that have increased in number. In cats it may be lymphocytes as well. Heavy exercise can have the same effect.

A second effect of stress takes a bit longer to develop. Your dog or cat ’s adrenal glands will also increase corticosteroid production when the pet is under stress. The same thing happens when those corticosteroids are given to your pet in pill or injection form to treat a health issue.

When that situation exits, the number of lymphocytes in your pets blood tend to go down while the number of neutrophils tend to go up. Again, it is the mature neutrophils (segs) that tend to rise the most. Veterinarians refer to both these phenomenon as a stress leukogram. Eosinophils and monocytes can rise a bit in this situation as well, but rarely as dramatically.

Folks tend to associate viral diseases with low leukocyte counts (leukopenia). But when things like bacterial pneumonia occur late in distemper infections or intestines become damaged from parvovirus, white blood cell numbers can actually go up. FIP in cats can cause a similar rise in neutrophil levels. In those cats, lymphocyte numbers generally go down. Those levels often persist until the pet either runs out of reserve WBCs or gets better.

Very high white blood cell counts can also occur due to bone marrow changes (hyperplasia) or cancer. In those cases, the WBCs liberated into the blood stream tend to be abnormal in appearance. That is when the trained eye of a veterinary clinical pathologist is so helpful. When those tumors are of the cell line (stem cells) that produce neutrophils, it will be only the neutrophil numbers that are high. But any one of the 5 types can be affected.

Young dogs and cats (before their first heat) tend to have higher WBC counts than older adults. Dogs brought to the vet in labor also tend to have high WBC counts. I do not know if that is due to the stress of labor, the fear associated with hospitalization, changes in their hormone levels or all those factors combined.

Reasons Why Your Pet’s White Blood Cell Count Could Be Low (leukopenia) :

The bone marrow of dogs and cats has a limited (finite) ability to produce white blood cells at an increased rate. Prolonged diseases of all kind can exhaust that ability. So after a sudden overwhelming infections or a ceaseless demand for WBCs over time, your pet’s bone marrow can simply run out of new WBCs to release into the pet's blood stream. That is particularly true of neutrophils (aka neutropenia).

Viral infections can cause total white blood cell numbers to go down. A moderate drop in number is often seen in coronavirus infection of dogs and infectious canine hepatitis. The drop is much more severe early in parvovirus infection of dogs and panleukopenia in cats.

WBC counts are often low in FIV-positive cats as well. Feline leukemia virus positive cats are not as predictable in their WBC numbers.

Space-occupying tumors of your pet’s bone marrow can squeeze out the cells that normally produce their WBC lines. Some of those tumors are of the cells that would actual produce WBCs (myelomas). However, the same tumors, on different occasion, also have the potential to release enormous numbers of defective WBCs into the pet’s circulation causing high WBC numbers.

Certain autoimmune diseases (primarily of dogs) cause pets to destroy their own WBCs (myelodysplastic syndromes). When that sort of problem is suspected in a dog, Ehrlichia infection needs to be ruled out, since the symptoms can be similar.

Many drugs used to treat cancer in dogs and cats have the potential to destroy the marrow cells that produce your pets WBCs. So does radiation therapy for those and other cancers.

Other medications that are known to occasionally cause low WBC numbers are: methimazole given to cats for hyperthyroidism (in 4-10%), certain antibiotics (eg trimethoprim-sulfa), medications to combat fever (dipyrone).

Clomipramine (Clomicalm), given to dogs for anxiety, has caused low WBC counts when given to humans for the same sort of problems. I am uncertain if that effects occurs in pets.

Estrogens given as the infamous “mismating”shot to female dogs also has that potential.

Ehrlichia infection, spread by ticks, can cause low WBC counts in dogs.

A genetic disease of grey collies called cyclic hematopoiesis will also cause WBC counts to drop about every 11-14 days. A similar condition sometimes occurs in blue-smoke-color Persian cats (Chediak-Higashi syndrome).

Greyhounds (possibly other sight hounds and Belgian Tervuren) tend to have lower normal WBC counts than other breeds (3.5-6.5 vs 6-17). So one needs to look for other signs of illness in interpreting blood data from those breeds.

Complementary Tests :

Begin with evaluation of the pet’s CBC and blood chemistry values. With that data in hand and your veterinarian’s physical examination, the possible tests that could be appropriate for your pet are too many for me to list. If the pet appears healthy in other respects, it is usually OK to wait a week or two and re-run the WBC count before pursuing other diagnostics.

.................... DxMe