Leukocyte Identification and Evaluation

Leukocyte Identification and Evaluation Overview

Leukocyte Identification and Leukogram

  • Leukocyte Identification: Process of identifying white blood cells (WBCs) in peripheral blood.

  • Leukogram: Quantification of leukocyte classes and morphologic abnormalities, determined by evaluating a peripheral blood smear.

Blood Smear Examination Protocol

  • Start at 40imes40 imes objective: Check for platelet clumps, enlarged cells, microfilariae.

  • Move to feathered edge: Check for cell clumping.

  • Move 3−43-4 fields inward to the monolayer: Cells are in a single layer, not overlapping.

  • Switch to 100imes100 imes objective: Perform differential cell count by counting 100100 WBCs to get percentages.

Absolute Values Calculation

  • Calculated after differential cell count and total WBC count are known.

  • Example: Total WBC 4.4imes109/L4.4 imes 10^{9}/L; Neutrophils 49%49\% means 4.4imes109/Limes0.494.4 imes 10^{9}/L imes 0.49 absolute neutrophils.

Major Leukocyte Types

Neutrophils ("Segs")

  • Nucleus: Irregular, elongated, lobed; mature form is segmented.

  • Function: Granulocytic cell, participates in inflammatory responses, phagocytosis.

  • Indicators: Increased numbers indicate inflammation/infection.

  • Granules: Small, poorly stained, colorless to lightly staining (species variations).

  • Heterophils: Replace neutrophils in reptiles, birds, some fish, rabbits, guinea pigs; granules are eosinophilic.

Band Neutrophils

  • Description: Immature neutrophil stage.

  • Nucleus: Smooth, parallel-sided, horseshoe-shaped with "clubbed ends," no constrictions. Narrowest part >2/32/3 widest part.

  • Normal Values: 0−3%0-3\% for all species.

Eosinophils

  • Nucleus: Similar to neutrophils.

  • Function: Immune system modulation, phagocytosis.

  • Hormones: Numbers increase with allergic reactions and parasitic infections.

  • Granules: Large, stain red, vary by species (e.g., canine have small to large light reddish, feline are rod-shaped reddish, equine are very large bright orange-red).

Basophils

  • Function: Involved in immune system mediation (inflammation, infection).

  • Occurrence: Not often found in peripheral blood smears.

  • Size: Larger than neutrophils.

  • Nucleus: Similar to monocytes.

  • Granules: Vary by species (e.g., canine have few dark purple-blue, feline have large round lavender, equine/bovine have many dark blue-black, may occlude nucleus).

  • Normal Values: 0−3%0-3\%.

Lymphocytes

  • Classification: Agranulocytic cell.

  • Function: Humoral and cell-mediated immune responses (antibody production).

  • Nucleus: Dark purple-blue, round to oval or slightly indented; clumping chromatin.

  • Cytoplasm: Small amount of clear to sky blue.

  • Prevalence: Most abundant cell in ruminant blood smears.

  • Indicators: Increase usually indicates viral infection.

Monocytes

  • Classification: Agranulocytic cells.

  • Size: Largest WBC.

  • Function: Participate in inflammatory response, phagocytize foreign material, responsible for erythrocyte destruction and iron recycling.

  • Indicators: Increased numbers with chronic infections.

  • Nucleus: Kidney-shaped with occasional lobes, lacy appearance, does not stain as dark as other cells.

  • Cytoplasm: Grey-blue, may contain small pink granules or vacuoles.

Monocyte vs. Lymphocyte Identification

  • Monocyte: Grey-blue cytoplasm (ground glass, tiny pink granules), deeply indented/amoeboid nucleus, large/small vacuoles, reticulated (lacy) chromatin.

  • Lymphocyte: True or sky-blue cytoplasm (rare large granules), round to slightly indented nucleus, extremely rare/tiny vacuoles, clumped chromatin.

Abnormal Leukocyte Morphology

Quantification Systems

  • Slight, Moderate, Marked: Slight (~10%10\%), Moderate (~25%25\%), Marked (>50%50\%) of cells affected.

  • 1+, 2+, 3+, 4+: 1+1+ (5−10%5-10\%), 2+2+ (10−25%10-25\%), 3+3+ (~50%50\%), 4+4+ (>75%75\%) of cells affected.

Specific Abnormalities

  • Nuclear Hypersegmentation: Neutrophils with >55 lobes, usually due to cell aging. Common.

  • Toxic Change: Most common disease-induced cytoplasmic change in neutrophils, associated with inflammation, infection, drug toxicity.

    • Features: Cytoplasmic basophilia, Döhle bodies (blue staining inclusions), vacuoles/foamy cytoplasm, toxic granulation (rare).

    • Quantification (Percentage of Neutrophils): Mild (5−10%5-10\%), Moderate (11−30%11-30\%), Marked (>30%30\%).

  • Intracytoplasmic Inclusions: Presence of material within the cytoplasm (e.g., Canine Distemper, Ehrlichia, Anaplasma, Histoplasma).

  • Reactive Lymphocytes (Immunocytes): Basophilic, more abundant cytoplasm, increased cell size, convoluted nucleus. Seen with antigenic stimulation (infection/vaccination).

  • Atypical Lymphocytes: Basophilic cytoplasm, increased cell size, cleaved nuclei, asynchronous maturation. Seen with chronic antigenic stimulation (e.g., Canine Ehrlichiosis).

  • Smudge/Basket Cells: Ruptured, degenerative leukocytes. Significant in large numbers (leukemia), can be an artifact.

  • Neoplasia (Leukemia):

    • Neoplastic proliferation of hematopoietic cells in blood and/or bone marrow.

    • Neoplastic Cell Types ("Type Cells"): Blast cells, atypical cells, bizarre cells, mitotic figures, unclassified neoplastic cells.

    • Mitotic Figures: When seen on blood smear, indicative of neoplasia.

    • Blast Cells: Confined to bone marrow normally, increased in neoplasia or present in blood smear.

    • Abnormal Lymphocytes: Vacuolated, clumped, or more basophilic.

Myeloproliferative Disease

  • Characterized by: Bone marrow hypercellularity, loss of maturation orderliness, abnormal (neoplastic) cells.

  • Features: Abnormal red blood cells (RBCs), WBCs, or platelets; increased WBCs, increased nucleated RBCs, decreased packed cell volume (PCV), abnormal cells, nonregenerative anemia, thrombocytopenia.

  • Common in cats with FeLV infection.

Lymphoproliferative Disorders

  • Description: Abnormal proliferation of lymphoid cells; tumors derived from lymphocytes or plasma cells.

  • More common than myeloproliferative disorders.

  • Associations: FeLV, FIV infection (cats), Bovine Leukosis Virus (BLV) (cattle).

  • Categories: Primary lymphoid leukemia, lymphoma, plasma cell tumors.

  • Differentiation: Polymerase chain reaction (PCR) can distinguish neoplastic vs. non-neoplastic.

  • Lymphoid leukemia: Neoplastic cells in bone marrow +/- blood.

  • Lymphoma: Neoplastic cells in solid tissue (tumors, e.g., lymph nodes).