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Hematology

Blood cells · Coagulation · Anemias · Clinical Lab Tests

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Blood Cell Types & Normal Values

Hemoglobin (Male)
13.5–17.5 g/dL
Hemoglobin (Female)
12–16 g/dL
WBC Count
4,000–11,000/µL
Platelet Count
150,000–400,000/µL
Hematocrit (Male)
41–53%
RBC Lifespan
~120 days

Anemia Classification by MCV

  • Microcytic (MCV < 80 fL) — Iron deficiency anemia, Thalassemia, Sideroblastic anemia, Lead poisoning
  • Normocytic (MCV 80–100 fL) — Acute blood loss, Hemolytic anemia, Aplastic anemia, Chronic disease anemia
  • Macrocytic (MCV > 100 fL) — Vitamin B12 deficiency, Folate deficiency, Liver disease, Hypothyroidism

White Blood Cell Differential

  • Neutrophils 50–70% — First responders to bacterial infection. Phagocytic. Hypersegmented in B12 deficiency.
  • Lymphocytes 20–40% — B-cells (antibody production), T-cells (cell-mediated immunity). Elevated in viral infections.
  • Monocytes 3–8% — Become macrophages in tissues. Phagocytic. Elevated in chronic infections.
  • Eosinophils 1–4% — Combat parasites, involved in allergic reactions. Elevated in parasitic infections & asthma.
  • Basophils 0–1% — Release histamine. Role in allergic responses. Least common WBC.

Coagulation Tests

  • PT (Prothrombin Time) — Tests extrinsic pathway (Factor VII) + common pathway. Normal: 11–13.5 sec. Used to monitor warfarin.
  • aPTT — Tests intrinsic pathway (XII, XI, IX, VIII) + common pathway. Normal: 25–35 sec. Used to monitor heparin.
  • INR — Standardized PT ratio. Normal: ~1.0. Therapeutic range on warfarin: 2–3.
  • Bleeding Time — Tests platelet function and vascular response. Normal: 1–9 minutes.
  • Fibrinogen — Normal: 200–400 mg/dL. Decreased in DIC and liver disease.
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Answer
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Q: What is the difference between serum and plasma?
Plasma is blood from which cells have been removed but clotting factors are retained (collected with anticoagulant). Serum is plasma from which fibrinogen and clotting factors have been removed after clotting. Plasma = blood − cells. Serum = plasma − clotting factors.
Q: What is the buffy coat and what does it contain?
The buffy coat is the thin white layer between plasma (top) and packed red cells (bottom) in centrifuged blood. It contains leukocytes (white blood cells) and platelets. It appears white/cream colored because these cells lack hemoglobin.
Q: Name the anticoagulants used in hematology and their tubes.
EDTA (Purple cap) — CBC, blood film, ESR. Chelates calcium. Sodium Citrate (Blue cap) — Coagulation studies (PT, aPTT). Ratio 9:1 blood:anticoagulant. Heparin (Green cap) — Electrolytes, blood gases. Activates antithrombin III. Fluoride Oxalate (Grey cap) — Glucose, lactate. Inhibits glycolysis.
Q: What is the principle of ESR (Erythrocyte Sedimentation Rate)?
ESR measures the rate at which RBCs settle in a vertical tube over 1 hour. In inflammation, elevated fibrinogen and globulins coat RBCs, promoting rouleaux formation (stacking like coins), which increases settling rate. Westergren method is standard. Normal: Males <15 mm/hr, Females <20 mm/hr.
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Coagulation Cascade

EXTRINSIC PATHWAY
Tissue Damage→ Tissue Factor (III)→ Factor VII activated→ Factor X ↓
INTRINSIC PATHWAY
Contact (XII)→ XI → IX → VIII→ Factor X ↓
COMMON PATHWAY
Factor X + V→ Prothrombin → Thrombin→ Fibrinogen → Fibrin→ Stable Clot ✓

Anemia Classification by MCV

MICROCYTIC
MCV <80
Iron deficiency
Thalassemia
Sideroblastic
NORMOCYTIC
80–100
Acute blood loss
Hemolytic
Aplastic
MACROCYTIC
MCV >100
B12/Folate def.
Liver disease
Hypothyroid

Complete Blood Count (CBC) Procedure

  • Specimen: EDTA whole blood (purple cap) — 3 mL minimum
  • Method: Automated hematology analyzer (e.g., Sysmex, Mindray)
  • Mix gently 8–10 times before analysis to prevent clumping
  • Stability: Stable at room temperature for 6 hours, refrigerated for 24 hours
  • Report includes: Hb, RBC, WBC, Platelets, HCT, MCV, MCH, MCHC, differential count
  • Quality control: Run controls (low, normal, high) at start of each shift

Peripheral Blood Film Preparation

  • Place small drop of blood 1 cm from end of slide
  • Spreader slide at 30–45° angle — push steadily in one motion
  • Film should have feathered edge and cover 2/3 of slide
  • Air dry completely before staining
  • Leishman stain: Flood slide → add buffer (pH 6.8) → 10–15 min → wash → dry
  • Examine under oil immersion (×100): count 100 WBCs for differential