Why Is My Dog Or Cat's Blood Neutrophil Count High Or Low ?













Ron Hines DVM PhD

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Your Pet's Neutrophils aka "Segs", "Matures", "POLYS", Granulocytes or more correctly = Polymorphonuclear Granulocytes = PMNs

Perhaps neutrophils have so many other names because they are so important. Whatever you call them, their main job is to defend your dog or cat ’s body against bacteria and other invaders. Neutrophils rapidly move through the pet's blood stream to the site of an infection, where they bind to and eat (phagocytize) bacteria and other unwanted agents that they encounter.

Unlike the other phagocytic cells, the monocytes, neutrophils live only a short time. Neutrophils are generated from stem cells in your dog or cat ’s bone marrow (pluripotent hematopoietic stem cells). Once neutrophils leave the marrow and enter the blood stream, they circulate for only a day, perhaps less, then they move into your pet’s tissues to live another 1-2 days before self-destructing (apoptosis). What is left of them is cleared away by the pet’s macrophages.



Neutrophils are formed and leave your pet’s bone marrow at a steady, constant rate – until an “emergency situation" occurs. When such a situation occurs healthy bone marrow stem cells are capable of producing neutrophils extremely rapidly. In that hurry-to-leave the number of band or young neutrophils entering the pet's blood often increases as well ("shift to the left" "shilling shift"). The more mature neutrophils (Segs), are recognized by their multi-lobed (lobulated) nucleus. Together, they circulate hugging the walls of small blood vessels (marginating cells) where they look for the chemicals released by damaged tissue, inflammation or invading microorganisms.

Your pet’s macrophages, monocytes and other policing cells also remain on the look out for invaders. When they sense them, they release chemicals that attract neutrophils (such as interkeukin-8). Neutrophils that rush to the rescue are the primary constituent of pus; such as what drains from the cavities of abscesses that occur so commonly after cat fights or around a splinter in your dog's paw.

With time, you pet’s lymphocytic system might produce antibodies against invaders , but its neutrophils are the first responders of its immune system.

Reasons Why Your Pet's Neutrophil Count Might Be High (Neutrophilia) :

High levels of neutrophils occur in many infections. But other forms of inflammation, such as wounds and surgery can elevate their numbers as well.

Sudden stress that stimulates your pet’s adrenal glands to liberate corticosteroid and epinephrine also raise neutrophil numbers (stress leukogram).

Autoimmune and allergic reactions can liberate chemicals (inflammatory cytokines) that cause high neutrophil numbers as well.

Corticosteroid medication (eg prednisone) can also elevate neutrophil numbers.

On rare occasion, a pet's continuing high neutrophil numbers are due to a tumor of the stem cells that produce them in the bone marrow (myelogenous leukemia).

Reasons Why Your Pet’s Neutrophil Count Might Be Low (Neutropenia, Agranulocytosis) :

When a pet’s infection is overwhelming, its bone marrow can simply run out of neutrophils. That can cause blood neutrophil numbers to drop. The same can occur when infectious organisms liberate large amounts of toxins (acute endotoxemia).

Any of the diseases, toxins or drugs that affects a pet’s bone marrow (see M:E ratio section) can also cause neutropenia.

Certain viral diseases (like Parvovirus in dogs and panleukopenia virus in cats) can cause low neutrophil numbers. Other viruses, (like dog distemper) are less predictable. When they do cause low neutrophil counts, it is usually early on in the infection.

Certain medications (eg methimazole in hyperthyroid cats, cephalosporin antibiotics like Keflex and other beta-lactam antibiotics), and anti-cancer medications such as cyclophosphamide can lower neutrophil numbers (probably through their effect on the bone marrow).

There is a much longer list of medications that can depress neutrophil numbers in humans; but I have no information as to what those meds might do to neutrophil numbers in your pet.

Complementary Tests :

CBC/WBC and blood chemistry panel, body temperature, further tests based on those results and your veterinarian's physical examination of your pet.