Leukocytes III: Neutrophils Continued

Vocabulary practice flashcards covering neutrophil kinetics (physiologic and corticosteroid-induced neutrophilia), mechanisms and thresholds of neutropenia, toxic change grading (1+ to 4+), and intracytoplasmic organisms observed in hematology.

Physiologic Leukocytosis

An epinephrine-mediated leukocytosis triggered by excitement or exercise ("fight or flight"), resulting from a shift of neutrophils from the marginal pool to the circulating pool; typically manifests as a neutrophilia ($2\times$) without a left shift, lasting seconds to $20\text{--}30\text{ minutes}$.

Corticosteroid-Induced Leukogram ("Stress Response")

A leukogram change caused by endogenous or exogenous glucocorticoids, characterized by neutrophilia (due to marrow storage release, marginal-to-circulating shift, and prolonged circulating lifespan), lymphopenia, eosinopenia, usually no left shift, and monocytosis (in dogs).

Sepsis Risk Threshold in Neutropenia

A circulating neutrophil count of $< 500\text{ neutrophils}/\mu\text{l}$, which places veterinary patients at immediate high risk for bacterial sepsis.

Radiomimetic Viruses

Viruses such as canine parvovirus, feline panleukopenia virus, and bovine viral diarrhea virus that damage rapidly dividing marrow precursors and cause neutropenia via decreased neutrophil production.

Cyclic Neutropenia (Cyclic Hematopoiesis)

A hereditary disorder of stem cell regulation leading to periodic decreased neutrophil production, classically recognized in grey collies.

Leukergy

The clumping and adherence of "sticky leukocytes" along blood vessels or on a smear, representing rapid sequestration into the marginal pool during the initial vascular response to endotoxemia.

Toxic Change (Neutrophil Toxicity)

Morphologic abnormalities of neutrophils and their precursors caused by increased inflammatory mediators, cytokines, or bacterial toxins during accelerated granulopoiesis; when marked, it is a key indicator of sepsis or severe bacterial infection.

Döhle Bodies

Pale blue-gray cytoplasmic inclusions consisting of aggregated rough endoplasmic reticulum and ribosomes; represents the earliest and mildest morphological sign of neutrophil toxic change.

Toxic Granulation

The retention of prominent purple or azurophilic primary granules in neutrophil cytoplasm; a rare manifestation of severe toxic change seen most frequently in horses (e.g., during Strangles / Streptococcus equi infections).

1+ Toxic Change

A mild grade of neutrophil toxicity characterized solely by the presence of Döhle bodies.

2+ Toxic Change

A moderate grade of neutrophil toxicity characterized by Döhle bodies accompanied by either diffuse cytoplasmic basophilia OR cytoplasmic vacuolation.

3+ Toxic Change

A marked grade of neutrophil toxicity characterized by Döhle bodies present alongside both diffuse cytoplasmic basophilia AND cytoplasmic vacuolation, with or without toxic granulation.

4+ Toxic Change

A severe grade of neutrophil toxicity in which morphologic alterations and cytoplasmic swelling are so pronounced that neutrophils cannot be reliably distinguished from monocytes.

Intracytoplasmic Bacteria in Neutrophils

An uncommon finding in circulating blood smears indicating overwhelming bacteremia or septicemia, carrying a poor prognosis.

Anaplasma phagocytophilum Morulae

Intracytoplasmic microcolonies (morulae) appearing as basophilic clusters within neutrophils on routine blood smears of infected dogs and horses (formerly classified as Ehrlichia equi).

Hepatozoon americanum

A tick-borne protozoal organism that appears as large, oval, capsule-like gamonts within the cytoplasm of circulating neutrophils in dogs.

Myelophthisis

The crowding out or replacement of normal hematopoietic tissue in the bone marrow by abnormal cells, fibrous tissue, or space-occupying lesions, leading to decreased neutrophil production and neutropenia.