Clinical Hematology - Blood's Cellular Elements - WBC, PLT

What are the 6 stages of neutrophil maturation in order?

1. Myeloblast

2. Promyelocyte

3. Myelocyte

4. Metamyelocyte

5. Band Neutrophil

6. Segmented Neutrophil

How do you differentiate a Promyelocyte from a Myelocyte?

• Promyelocyte: Primary/azurophilic granules appear (MPO+); nucleoli present.

• Myelocyte: Secondary/specific granules appear; nucleoli absent; last stage capable of mitosis.

How do you morphologically distinguish a Metamyelocyte, Band, and Segmented Neutrophil?

• Metamyelocyte: Indented/kidney-bean shaped nucleus (indentation <50% of width).

• Band: C/U-shaped nucleus with parallel sides (indentation >50%).

• Segmented: 2–5 distinct nuclear lobes connected by thin thread-like chromatin filaments.

What are the two major bone marrow pools of neutrophils?

• Mitotic Pool: Myeloblasts, promyelocytes, myelocytes (proliferating).

• Post-Mitotic Pool: Metamyelocytes, bands, segs (maturation and 5–7 day storage reserve).

What is the difference between the Circulating and Marginating Granulocyte Pools (CGP & MGP)?

• CGP (50%): Neutrophils actively flowing in axial blood (measured by CBC).

• MGP (50%): Neutrophils loosely adhered to vascular endothelium.

• Epinephrine/stress causes rapid pseudoneutrophilia by shifting MGP to CGP.

What are the steps of neutrophil host defense and phagocytosis?

1. Chemotaxis & Migration (C5a, LTB4, IL-8$)

2. Adhesion & Diapedesis (Selectins → ß₂-integrins/ICAM-1)

3. Opsonization & Ingestion (IgG/C3b via Fc/CR1 receptors)

4. Degranulation & Phagolysosome Formation

5. Bactericidal Killing

How does oxygen-dependent killing (respiratory burst) work in neutrophils?

NADPH oxidase generates superoxide (·O₂^-) → SOD converts it to H₂O₂ → Myeloperoxidase (MPO) converts H₂O₂ + Cl^- into toxic hypochlorous acid (HOCl).

What are the morphological characteristics and primary functions of Eosinophils?

• Morphology: Bilobed nucleus with large, uniform, reddish-orange granules.

• Contents: Major Basic Protein (MBP), Eosinophil Peroxidase (EPO), Histaminase.

• Function: Defense against helminthic/parasitic infections and modulation of allergic responses.

What are the morphological characteristics and primary functions of Basophils?

• Morphology: 2–3 lobed nucleus obscured by coarse, dark purple-black granules.

• Contents: Histamine, Heparin, Leukotriene C4 (LTC₄).

• Function: Key mediator of Type I immediate hypersensitivity reactions via high-affinity FcεRI IgE receptors.

How do you calculate the Absolute Neutrophil Count (ANC)?

ANC = Total WBC × (% Segs + % Bands) ÷ 100

What is a "Left Shift" and how do Regenerative vs. Degenerative shifts differ?

• Left Shift: Increased immature neutrophil precursors (bands, metamyelocytes) in blood.

• Regenerative: High WBC count + left shift (appropriate marrow response to infection).

• Degenerative: Low/normal WBC count + high immature % (marrow exhaustion/severe sepsis; poor prognosis).

What are the key surface immunophenotypes (CD markers) for B cells, T cells, and NK cells?

• B Cells: CD19, CD20, CD21, CD22, sIg

• T Cells: CD2, CD3, CD5, CD7 (CD4⁺ Helper, CD8⁺ Cytotoxic)

• NK Cells: CD16 (ADCC), CD56; lacks CD3

How do resting lymphocytes, reactive lymphocytes, LGLs, and plasma cells differ morphologically?

• Resting: Small, high N:C ratio, dense clumped chromatin, thin rim of blue cytoplasm.

• Reactive: Large, abundant cytoplasm that scallops/hugs adjacent RBCs with peripheral basophilia.

• LGLs: Pale blue cytoplasm containing distinct azurophilic granules (NK or CD8⁺ T cells).

• Plasma Cell: Eccentric nucleus with "clock-face" chromatin, intensely basophilic cytoplasm, and a prominent perinuclear halo.

How does lymphocyte distribution in blood differ between children and adults?

• Pediatrics (6 mos–2 yrs): Lymphocyte-predominant (~60% of WBCs; normal absolute count up to 9.5 x 10³/uL)

• Adults: Neutrophil-predominant (Lymphocytes 20–40%; normal absolute count 1.0-4.8 × 10³/uL).

What defines Absolute Lymphocytosis vs. Lymphocytopenia in adults?

• Absolute Lymphocytosis: >4.8 x 10³ uL (>4.8 × 10⁹/L) (e.g., EBV, Pertussis, CLL).

• Absolute Lymphocytopenia: <1.0 x 10³/ uL (<1.0 x 10⁹/L) (e.g., HIV/AIDS, corticosteroids, SCID).

What are the key diagnostic identifiers of a mature Monocyte?

Largest WBC in blood; folded/brain-like/horseshoe nucleus with loose lacy chromatin; dull gray-blue ("ground glass") cytoplasm with fine azurophilic granules and vacuoles; CD14⁺ and Non-Specific Esterase (NSE) positive.

What are the organ-specific tissue macrophages for Liver, Lungs, CNS, Bone, and Spleen?

• Liver: Kupffer Cells

• Lungs: Alveolar Macrophages ("Dust Cells")

• CNS: Microglia

• Bone: Osteoclasts

• Spleen: Splenic Macrophages (red pulp)

What are the three core immunological roles of Monocytes/Macrophages?

1. Phagocytosis (scavenging debris/pathogens via TLRs, Fc, and CR receptors).

2. Antigen Presentation (APC presenting via MHC Class II with CD80/CD86 to CD4⁺ T cells).

3. Cytokine Secretion (Pro-inflammatory: IL-1ß, TNF-α, IL-6; Anti-inflammatory: IL-10, TGF-ß).

How do you distinguish a Monocyte from a Reactive Lymphocyte on a blood smear?

• Monocyte: Uniform gray-blue "ground glass" cytoplasm, loose lacy chromatin, NSE positive.

• Reactive Lymphocyte: Clear/dark blue cytoplasm that flares at edges and hugs RBCs, coarse clumped chromatin, NSE negative.

What is Endomitosis in megakaryopoiesis and how does TPO regulate it?

DNA replication without nuclear or cytoplasmic division (2N → 32N). Thrombopoietin (TPO), made constitutively by the liver, binds the c-MPL receptor on platelets; low platelet counts leave more free TPO to stimulate marrow megakaryocytes.

Where are platelets distributed in the body, and what is the clinical significance of Reticulated Platelets?

• Distribution: ~67% in circulating blood, ~33% sequestered in the spleen.

• Reticulated Platelets (IPF): Newly released platelets containing mRNA (MPV > 12 fL). High IPF indicates peripheral destruction (e.g., ITP); Low IPF indicates bone marrow suppression.

What are the 3 steps of primary hemostasis and their key receptor/ligand pairs?

1. Adhesion: Subendothelial Collagen → vWF → GPIb/IX/V rece[tpr

2. Activation & Secretion: Shape change + release of ADP, Serotonin, Ca²⁺ (Dense granules) and vWF, Fibrinogen (Alpha granules) + T_xA₂ synthesis via COX-1.

3. Aggregation: Fibrinogen crosslinks activated GPIIb/IIIa receptors on adjacent platelets.

What causes EDTA-Induced Pseudothrombocytopenia and how is it resolved?

EDTA exposes cryptic GPIIb/IIIa epitopes, causing autoantibodies to aggregate platelets in vitro. Corrective action: Redraw blood in a Sodium Citrate (blue-top) tube and multiply the result by 1.1 (to correct for liquid anticoagulant dilution).