Understanding Abnormal Changes in the Leucogram Requires a Firm Understanding of Normal

 Normal leucocytes and their function:

 Granulocytes: neutrophils; eosinophils/ basophils

 Lymphocytes

 Monocytes

 Leucocyte dynamics: normal resting state, inflammation, stress, excitement

 Abnormal leucocytes--leukaemia

Normal Leucocytes

Neutrophils

 Most common granulocyte in circulation in dog and cat

 'Neutral' staining granules (granules contain enzymes and antibacterial substances to kill and degrade bacteria)

 Primary function:

 Primary defense against bacterial disease

 Can cause considerable 'innocent bystander' damage to tissues.

Eosinophils

 Function still a bit of a mystery:

 Granules contain proteins that bind to parasites (major basic protein)

 Very 'caustic'--causes tissue necrosis

 Associated with complex parasites: nematodes, fungi, some protozoans

 Regulate allergic reactions

 Associated with immune-complex disease

Basophils

 Function not understood

 Granules are similar to mast cell granules in content

 Uncommon in circulation

 Tend to increase in number in association with eosinophils

Lymphocytes

 Second most common circulating leucocyte in dogs and cats

 Primary function: immunity:

 Two basic types: B-cells (produce antibody), T-cells (regulate immune responses)

 Types not morphologically different

 Can change morphology when immune system is stimulated

Monocytes

 Phagocytosis (bacteria, complex organisms (fungal elements, protozoans), cellular debris associated with tissue necrosis)

 Regulate repair of tissues, regulate immune responses

 Major cell involved in red blood cell turnover and iron recycling

The Leucogram: Numerical and Morphological Characterisation of Circulating Leucocytes

White blood cell (WBC) count includes a differential cell count and morphological description of cells. In the differential count 100 cells are categorised by type (200 cells should be counted if the WBC count is >30.0 x 10⁹/l). Unclassified cells should be included in differential.

Note abnormal morphology: toxic change, abnormal granules, reactive lymphocytes or atypical cells.

Neutrophil Dynamics: Describes the Normal Flow of Leucocytes From the Bone Marrow to Peripheral Blood

Leucocyte Compartments

 Proliferating pool

 Maturation/storage pool

 Circulating/ marginated pool

Inflammatory Leucogram

 Band neutrophils are the hallmark of inflammation

 Neutrophils toxicity is the hallmark of sepsis:

 Dog--basophilic foamy cytoplasm and Döhle bodies

 Cat--basophilic foamy cytoplasm (Döhle bodies are commonly seen in cat neutrophils with no evidence of toxicity)

 Variation in band neutrophil morphology: dog and cat band neutrophils are not as segmented as horse or human

Regenerative Left Shift

 Regenerative--leucocytosis with greater number of mature neutrophils compared to bands

 Occurs when the bone marrow can keep up with the demand for neutrophils

 Chronic inflammation, focal inflammation

Degenerative Left Shift

 Greater number of bands than mature neutrophils, regardless of total count

 Normal or low count with significant numbers of bands

 Occurs when the bone marrow is overwhelmed

 Severe inflammation associated with large organ (e.g., pneumonia)

 Severe inflammation with loss of large amount of exudate (open pyometra, severe generalised exudative dermatitis)

Excitement (Epinephrine/Adrenaline)

 Associated with increases in lymphocytes as well

 Increase in blood pressure 'washes' marginated neutrophils off the vessel wall into circulating pool

 Also associated with increase in lymphocytes (lymphocytosis) that may exceed the neutrophilia

 More prominent in cats (have a larger marginated pool)

 No change in the other cell compartments

Stress (Steroid Leucogram)

 Does not have a left shift, mature neutrophilia, associated with lymphopenia

 Increased release of neutrophils from storage pool

 Neutrophils are less 'sticky' and move from the marginated pool to the circulating pool

 Increased retention of neutrophils in the circulation

 Steroids make neutrophils less flexible, they can't squeeze between the cells lining blood vessels

 Lymphopenia--lymphocytes can't get into blood vessels

 Monocytosis--mechanism unknown--seen in the dog

 Eosinopenia--mechanism unknown

Endotoxic (Gram-Negative) Sepsis

 Makes neutrophils very 'sticky'

 Increases marginated pool

 Increases exit from the blood vessel to tissue

 Decreases proliferation and maturation

 Often associated with a remarkable 'rebound' neutrophilia with a left shift

Lymphocytosis

 Excitement:

 All small normal appearing lymphocytes, usually <20,000/µl, transient

 Post vaccination (young dogs/cats):

 Small normal-appearing lymphocytes

 Occasional large immunoblasts

 Leukaemia:

 Chronic lymphocytic

 Acute lymphoblastic

 Chronic canine ehrlichiosis (tick fever)

Lymphopenia

 Stress

 Loss of lymphocytes (chylothorax, protein-losing enteropathy)

 Viral disease

 Genetic immune deficiency diseases

Monocytosis

 Result of stress, chronic inflammation, tissue necrosis

 Monocytopenia is not a problem

Eosinophilia

 Allergy, parasitism, fungal disease, neoplasia (mast cell tumour), hypereosinophilic syndrome

 Most commonly allergic dermatitis, asthma (idiopathic or parasitic), eosinophilic enteritis (idiopathic or parasitic), heartworm disease

Atypical Circulating Cells

 Reactive lymphocytes: antigenic stimulation

 Neoplastic cells:

 Myeloid--neutrophil origin

 Lymphoid--lymphocyte origin

 Myelomonocytic--both neutrophils and monocytes

 Monocytoid--monocyte origin

 Erythroleukaemia--red cell origin

 Genetic abnormalities--Pelger-Huët anomaly (decreased lobulation of granulocyte nuclei, not associated with disease), Chédiak-Higashi syndrome (abnormal fusion of lysosomes), lysosomal storage diseases (abnormal lysosomal enzymes)