wbc hematology notes

LEUKOCYTES (White Blood Cells)

Overview

  • Leukocytes, commonly called white blood cells (WBCs), play a crucial role in the immune system by protecting the body against infection and foreign invaders.

WBC Differentiation

  • Differential WBC Count: A laboratory technique used to determine the proportion of different types of leukocytes in the blood.

    • Useful for establishing differential diagnoses.

    • At least 100 leukocytes should be classified and counted in the counting area of a blood smear.

    • Calculation of Absolute Count:

    • ext{Absolute Count} = ext{% each cell type} imes ext{total WBC (in mcg/L of blood)}

    • Notable species variation in leukocyte counts.

Classifications of WBCs

  • Leukocytes can be classified primarily into two categories: Granulocytes and Agranulocytes.

    1. Granulocytes: Have a lobed nucleus and granules in the cytoplasm.

    • Include:

      • Neutrophils

      • Eosinophils

      • Basophils

    1. Agranulocytes: Have a single nucleus without granules.

    • Include:

      • Lymphocytes

      • Monocytes

Granulocytes

  • Characteristics:

    • Lobed nucleus and granules in cytoplasm with varying staining affinities.

    • Commonly produced in the bone marrow along with red blood cells from stem cells.

  • Types:

    • Neutrophils:

    • Prevalence: Most common leukocyte in dog and cat blood (50-70%).

    • Maturation: Takes 5-7 days to mature in bone marrow.

    • Circulation: Normally present in circulation for 8-10 hours.

    • Function: Primary defense against bacteria and inflammation.

    • Neutrophilia: An increase in neutrophil numbers due to infection, stress (glucocorticoids), or excitement (epinephrine).

    • Appearance: Nucleus irregular and ragged with 3-4 lobes; coarse and clumped chromatin; faint pink-gray cytoplasm; dark coarse granules (toxic granulations) indicate inflammation.

    • Eosinophils:

    • Prevalence: Make up 2-5% of WBCs in normal dogs.

    • Function: Detoxify injured tissues, containing antihistamines to neutralize toxins, and possess phagocytic abilities.

    • Appearance: Stain pink with eosin; different shapes of granules across species.

    • Basophils:

    • Prevalence: Rarely seen (<1% in blood).

    • Function: Contain histamine and heparin, involved in inflammatory responses.

    • Appearance: Larger than neutrophils with fewer lobes; granules dissolve in the stain preparation; cause inflammation via histamine release.

Agranulocytes

  • Lymphocytes:

    • Prevalence: Second most common leukocyte (12-30%).

    • Function: Specific immune response through T-lymphocytes (killer, helper, suppressor) and B-lymphocytes (plasma cells and memory cells).

    • Appearance: Dark blue nucleus, minimal clear cytoplasm.

  • Monocytes:

    • Prevalence: Consist of 3-5% of circulating WBCs.

    • Function: Phagocytosis of pathogens and debris; release chemicals to recruit neutrophils.

    • Appearance: Large with irregular kidney-shaped nuclei; blue-gray cytoplasm with a "ground glass" appearance.

Plasma Cells

  • Description: Nucleated cells that are oval/round, often confused with lymphocytes.

  • Function: Synthesize, store, and release immunoglobulins.

  • Prevalence: Rare (<1% of nucleated cells in bone marrow).

Leukocyte Normal Ranges (Blood Values)

  • Canine:

    • Neutrophil: 60-70% / Absolute: 3-11.4 x 10³/μL

    • Band Neutrophil: 0-3% / Absolute: 0-0.3 x 10³/μL

    • Lymphocyte: 12-30% / Absolute: 1-4.8 x 10³/μL

    • Monocyte: 3-10% / Absolute: 0.15-1.35 x 10³/μL

    • Eosinophil: 2-10% / Absolute: 0.1-0.75 x 10³/μL

    • Basophil: Rare

  • Feline:

    • Neutrophil: 35-75% / Absolute: 2.5-12.5 x 10³/μL

    • Band Neutrophil: 0-3% / Absolute: 0-0.3 x 10³/μL

    • Lymphocyte: 20-55% / Absolute: 1.5-7 x 10³/μL

    • Monocyte: 1-4% / Absolute: 0-0.85 x 10³/μL

    • Eosinophil: 2-12% / Absolute: 0-0.75 x 10³/μL

  • Rabbit:

    • Neutrophil: 20-75% / Absolute: 1-9.4 x 10³/μL

    • Band Neutrophil: NDA

    • Lymphocyte: 30-85% / Absolute: 1.6-10.6 x 10³/μL

    • Monocyte: 1-4% / Absolute: 0.05-0.5 x 10³/μL

    • Eosinophil: 1-4% / Absolute: 0.05-0.5 x 10³/μL

    • Basophil: 1-7 x 10³/μL

Differentiating Leukocytes

  • Several criteria can be used to differentiate leukocytes:

    • Cell Size

    • Nuclear Shape: Round, lobed, or segmented.

    • Cytoplasm Color: Pink, blue, gray, lavender.

    • Nucleus: Cytoplasm Ratio

    • Cytoplasm Texture: Smooth, grainy.

    • Cytoplasm Granules: Shape, size, color.

    • Chromatin Pattern: Loose, clumped.

WBC Terminology

  • Leukocytosis: An increase in white blood cell count, commonly associated with infection, hemorrhage, pregnancy, and toxemias.

  • Leukopenia: A decrease in white blood cell count, often linked to viral infections.

    • Suffixes:

    • -osis: Increase, invasion

    • -penia: Decrease, deficiency

    • pan-: All

Left Shift and Right Shift

  • Left Shift: Indicates a higher demand for neutrophils than what the bone marrow can supply mature forms of, leading to an overall increase in immature forms (bands and metamyelocytes).

    • Typically indicates an inflammatory response.

  • Right Shift: Refers to an increase in mature neutrophils with 5+ lobes due to prolonged circulation, seen in conditions such as Cushing’s disease or as an artifact of older blood.

Summary Comparison: RBCs vs WBCs

  • Function: RBCs are primarily for gas transport (O2 & CO2), while WBCs protect against disease invasion.

    • Approximate Count: 6-10 million RBCs per cu. mm vs 6-18 thousand WBCs per cu. mm in dogs.

  • Presence of Nucleus: RBCs do not have a nucleus; WBCs do.

  • Presence of Hemoglobin: RBCs contain hemoglobin, leukocytes do not.

  • Life Span: RBCs live about 100-120 days (1% replaced daily); WBCs have a variable lifespan (20-30 days typically).

  • Capillary Escape: WBCs can escape capillaries, but RBCs cannot.