How do you interpret a Complete Blood Count (CBC) blood smear?

How to Interpret CBC Blood Smear

A visual review of the peripheral blood smear is critical to confirm the size, shape, and color of red blood cells and should be performed as part of a complete blood count (CBC) interpretation to ensure accurate diagnosis and appropriate clinical management. 1

Red Blood Cell Evaluation

• Classify anemia based on Mean Corpuscular Volume (MCV) as microcytic (<80 fL), normocytic (80-100 fL), or macrocytic (>100 fL) to narrow differential diagnosis 2, 1
• Assess red blood cell morphology for:
  • Size variations: microcytosis, macrocytosis, anisocytosis (variation in size) 3
  • Shape abnormalities: spherocytes (hemolytic anemia), schistocytes (microangiopathic hemolytic anemia), sickle cells (sickle cell disease), target cells (liver disease, hemoglobinopathies) 3
  • Color/hemoglobinization: hypochromia (iron deficiency), hyperchromia (spherocytosis) 3
  • Inclusions: Howell-Jolly bodies (asplenia), basophilic stippling (lead poisoning, thalassemia), Heinz bodies (oxidative stress) 3
• Evaluate reticulocyte count to distinguish between decreased production and increased destruction/loss of red blood cells 1

White Blood Cell Evaluation

• Assess total white blood cell count for leukocytosis or leukopenia 1
• Evaluate neutrophil morphology for:
  • Left shift (increased band forms) suggesting bacterial infection 1
  • Toxic granulation, Döhle bodies, or cytoplasmic vacuolization indicating inflammation or infection 4
  • Hypersegmentation (>5 lobes) suggesting megaloblastic anemia or myelodysplastic syndrome 4
• Examine lymphocyte morphology for:
  • Atypical lymphocytes (viral infections, particularly infectious mononucleosis) 1
  • Abnormal lymphocytes suggesting leukemia or lymphoma 4
• Look for eosinophilia which may indicate allergic reactions, parasitic infections, or certain neoplasms 2, 1
• Note basophilia which may suggest myeloproliferative disorders 2

Platelet Evaluation

• Assess platelet count for thrombocytopenia or thrombocytosis 1
• Evaluate platelet size (large platelets may indicate increased production) 4
• Look for platelet clumping (which may cause falsely low automated counts) 5
• Check for platelet satellitism around neutrophils (pseudothrombocytopenia) 4

Reporting Considerations

• Report both percentages and absolute counts when available for immunophenotyping results 2, 1
• Correct for lymphocyte purity when reporting immunophenotyping results 2
• For optimal quality, at least 90% lymphocyte purity should be observed within the lymphocyte gate (minimally 85%) 2

Common Pitfalls to Avoid

• Failing to review the blood smear when automated analyzers flag abnormal results 5
• Overlooking significant morphologic findings that automated analyzers cannot detect 5
• Misinterpreting artifacts (such as echinocytes from EDTA exposure) as pathologic findings 4
• Relying solely on automated CBC results without manual verification in clinically ill patients 5
• Ignoring the significance of left shift in neutrophils even when total white blood cell count is normal 1

Algorithmic Approach to Blood Smear Interpretation

1. Verify automated CBC results with blood smear scan 4
2. Perform manual differential count if abnormalities are flagged 4
3. Evaluate red cell morphology to classify anemia and narrow differential diagnosis 2, 3
4. Assess white cell morphology for signs of infection, inflammation, or malignancy 1
5. Examine platelet number and morphology 1
6. Correlate findings with clinical presentation and other laboratory results 6

By following this structured approach to blood smear interpretation, clinicians can extract valuable diagnostic information that complements automated CBC results and guides appropriate clinical management 6, 4.