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πŸ”¬ Complete Blood Count Interpretation

Overview

The Complete Blood Count (CBC) is one of the most commonly ordered tests, providing crucial information about three cell lines: RBCs, WBCs, and platelets.

🩸 Red Blood Cell Parameters

Hemoglobin & Hematocrit

Parameter Male Normal Female Normal Clinical Significance
Hemoglobin 13.5-17.5 g/dL 12.0-15.5 g/dL O2 carrying capacity
Hematocrit 41-53% 36-46% RBC volume percentage

RBC Indices

  • MCV (Mean Corpuscular Volume): 80-100 fL
  • <80: Microcytic β†’ Iron Deficiency, Thalassemia
  • 80-100: Normocytic β†’ Anemia of Chronic Disease, acute blood loss

  • 100: Macrocytic β†’ B12 Deficiency, Folate Deficiency

  • MCH (Mean Corpuscular Hemoglobin): 27-31 pg

  • MCHC (Mean Corpuscular Hemoglobin Concentration): 32-36 g/dL
  • RDW (Red Cell Distribution Width): 11.5-14.5%
  • Elevated in mixed anemias, early deficiency states

βšͺ White Blood Cell Parameters

Total WBC Count

  • Normal: 4,500-11,000 cells/ΞΌL
  • Leukocytosis: >11,000
  • Leukopenia: <4,500

Differential Count

Cell Type Normal % Absolute Count Increased In Decreased In
Neutrophils 50-70% 2,500-7,500 Bacterial infection, inflammation Chemotherapy, viral
Lymphocytes 25-40% 1,500-4,000 Viral infection, CLL HIV, steroids
Monocytes 2-8% 200-800 Chronic infection, TB Rare
Eosinophils 1-4% 50-400 Allergies, parasites Steroids
Basophils 0.5-1% 25-100 CML, allergies Hyperthyroidism

Left Shift

  • Increased bands (>5%) or immature neutrophils
  • Suggests acute bacterial infection or inflammation

πŸ”΅ Platelet Parameters

Platelet Count

  • Normal: 150,000-400,000/ΞΌL
  • Thrombocytopenia: <150,000
  • Mild: 100,000-150,000
  • Moderate: 50,000-100,000
  • Severe: <50,000 (bleeding risk)
  • Critical: <20,000 (spontaneous bleeding)
  • Thrombocytosis: >400,000

MPV (Mean Platelet Volume)

  • Normal: 7.5-11.5 fL
  • Large platelets: Young, increased production
  • Small platelets: Older, decreased production

πŸ“Š Clinical Approach to CBC Abnormalities

Anemia Workup

graph TD
    A[Low Hgb/Hct] --> B[Check MCV]
    B -->|<80| C[Microcytic]
    B -->|80-100| D[Normocytic]
    B -->|>100| E[Macrocytic]
    C --> F[Iron studies, Hgb electrophoresis]
    D --> G[Reticulocyte count]
    E --> H[B12, Folate, TSH]

Pancytopenia Differential

🚨 Critical Values

  • Hgb <7 g/dL or >20 g/dL
  • WBC <1,000 or >50,000/ΞΌL
  • Platelets <20,000 or >1,000,000/ΞΌL
  • Blasts or malignant cells present

πŸ’‘ Pearls for Interpretation

  1. Always correlate with clinical picture
  2. Check peripheral smear for abnormalities
  3. Consider physiologic variations:
  4. Pregnancy: Mild anemia, leukocytosis
  5. Altitude: Increased Hgb/Hct
  6. Smoking: Increased Hgb/Hct
  7. African ancestry: Lower WBC baseline

πŸ“š Quick Reference Algorithm

  1. Identify abnormal values
  2. Look for patterns (single vs multiple cell lines)
  3. Check indices (MCV for anemia, differential for WBC)
  4. Consider clinical context
  5. Order appropriate follow-up tests

This reference integrates knowledge from Hematology-Oncology Hub, Clinical Foundations Hub, and Laboratory Medicine