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Interpreting Peripheral Blood Smears

Section 9 Hematologic Alterations | Part 2 – Cardinal Manifestations & Presentation · Part 2 – Cardinal Manifestations & Presentation · Chapter 65

Key Clinical Points

  1. Examine peripheral blood smear at the feathered edge where cells lie in a single layer without overlapping.
  2. RDW Calculation: (standard deviation of MCV ÷ mean MCV) imes 100; Normal = 11–14%, High = 15–18% (indicates morphologic anisocytosis).
  3. Basophilic stippling: Diffuse fine/coarse blue dots (RNA residue); common in lead poisoning, thalassemia, and sideroblastic anemia.
  4. Howell-Jolly bodies: Dense blue circular nuclear remnants; indicates defective splenic function (e.g., splenectomy or functional asplenia).
  5. Polychromophilia: Bluish hue in red cell cytoplasm reflecting ribosomes in young red cells.
  6. Spherocytes: Small red cells without central pallor; seen in hereditary spherocytosis, hemolytic anemias, and clostridial sepsis.
  7. Schistocytes: Helmet-shaped cells; reflect microangiopathic hemolytic anemia (MAHA) or mechanical fragmentation (e.g., artificial heart valve).
  8. Hypersegmented neutrophils: ≥ 5 segmented nuclear lobes; commonly seen with folic acid or vitamin B12 deficiency.
  9. Target cells: Bull's-eye appearance; seen in thalassemia, iron deficiency, cholestatic liver disease, and hemoglobinopathies (e.g., HbC).
  10. Acanthocytes: Spiculated cells with irregular membrane projections; irreversible; seen in renal disease, abetalipoproteinemia, and splenectomy.
  11. Echinocytes: Spiculated cells with evenly spaced spikes; reversible; seen in renal failure, malnutrition, or as an artifact of stored blood.
  12. Döhle bodies: Discrete blue-staining nongranular areas (rough endoplasmic reticulum) in neutrophil periphery; signify infection or toxic states.
  13. Pelger-Hüet anomaly: Benign disorder with bilobed granulocytes; nucleus has spectacle-like or 'pince-nez' configuration.
  14. Rouleaux formation: Red cells align in stacks; related to increased serum protein levels.
  15. Platelet clumping: Can cause falsely low automated counts; often caused by anticoagulant used during collection.

DEFINITION & OVERVIEW

• Examination Technique: ◦ Location: Examine at the feathered edge where cells lie in a single layer. ◦ Magnification: Use an oil immersion lens (100-fold magnification). ◦ Sample Preparation: Request Wright-stained peripheral blood smears for optimal visualization. • Platelet Assessment: ◦ Manual Count: Count platelets in 5–6 fields, average the number per field, and multiply by 20,000 to estimate total count. ◦ Morphology: Normal platelets are 1–2 μm with a blue granulated appearance. ◦ Clinical Indicators: ◦ Large/Giant Platelets: Suggest rapid turnover or myeloproliferative disorders (e.g., primary thrombocythemia). ◦ Clumping: Often caused by anticoagulant; leads to falsely low automated counts. ◦ Fragmentation: Neutrophil fragments can cause falsely high automated counts. ◦ Granule Absence: May be an artifact, marrow disease, or gray platelet syndrome. • Red Cell Size Reference: ◦ Comparison: Use the nucleus of a small lymphocyte as a reference (both are typically ~8 μm wide). ◦ Microcytosis: Cells smaller than the lymphocyte nucleus. ◦ Macrocytosis: Cells larger than the lymphocyte nucleus; often more oval (macroovalocytes). • Morphological Indices: ◦ Anisocytosis: Variation in red cell size. ◦ Poikilocytosis: Variation in red cell shape.

ETIOLOGY & PATHOPHYISIOLOGY

• Red Cell Size Pathophysiology: ◦ Microcytosis: Result of iron deficiency, thalassemia, or anemia of chronic disease. ◦ Macrocytosis: Result of vitamin B12/folate deficiency, liver disease, alcoholism, or hypothyroidism. ◦ Anisocytosis: Measured by RDW; high RDW (15–18%) indicates significant size variation. • Red Cell Shape Pathophysiology: ◦ Spherocytes: Loss of membrane surface area relative to volume (Hereditary spherocytosis, hemolytic anemia, clostridial sepsis). ◦ Dacrocytes: Teardrop shape from marrow infiltration or fibrosis (myelofibrosis, MDS). ◦ Schistocytes: Fragmentation from microangiopathic processes or mechanical shearing (heart valve). ◦ Echinocytes: Reversible changes from osmotic/metabolic stress (renal failure, malnutrition). ◦ Acanthocytes: Irreversible changes from lipid metabolism disorders (renal disease, abetalipoproteinemia, splenectomy). ◦ Elliptocytes: Membrane protein defects or acquired conditions (iron deficiency, MDS, thalassemia). ◦ Stomatocytes: Membrane defects or osmotic changes (alcoholism, artifact of dehydration). ◦ Target cells: Excess membrane relative to hemoglobin content (thalassemia, liver disease, HbC). • Red Cell Inclusion Pathophysiology: ◦ Basophilic stippling: RNA residue from ribosomal aggregation (lead poisoning, thalassemia, sideroblastic anemia).

◦ Howell-Jolly bodies: Nuclear remnants from defective splenic function (splenectomy, functional asplenia). ◦ Nucleated red cells: Premature release from marrow; indicates myelophthisic process or severe hemolysis. ◦ Heinz bodies: Precipitated denatured hemoglobin under oxidative stress (G6PD deficiency). • Platelet Pathophysiology: ◦ Giant Platelets: Rapid turnover or myeloproliferative disorders (primary thrombocythemia). ◦ Clumping: Artifact of anticoagulant usage. ◦ Granule Absence: Gray platelet syndrome or handling artifact. • White Cell Pathophysiology: ◦ Döhle bodies: Rough endoplasmic reticulum aggregates in infections/toxic states. ◦ Pelger-Hüet anomaly: Benign disorder with bilobed granulocytes (spectacle-like). ◦ Chédiak-Higashi disease: Giant granules due to dynein defect (impaired vesicle trafficking). ◦ Hypersegmented neutrophils: ≥ 5 nuclear lobes; indicates folate or B12 deficiency.

CLINICAL FEATURES

• Red Cell Morphology: ◦ Size: Microcytic (<8 μm) vs. Macrocytic (>8 μm). ◦ Color: Normochromic (normal) vs. Hypochromic (pale; indicates low hemoglobin content). ◦ Shape: Poikilocytosis (Spherocytes, Dacrocytes, Schistocytes, Echinocytes, Acanthocytes, Elliptocytes, Stomatocytes, Target cells). • Red Cell Inclusions: ◦ Basophilic stippling: Fine/coarse blue dots; hallmark of lead poisoning. ◦ Howell-Jolly bodies: Dense blue circular inclusions; indicator of asplenia. ◦ Nucleated red cells: Prematurely released nuclei; indicates marrow stress or myelophthisis. ◦ Heinz bodies: Precipitated hemoglobin (requires crystal violet for visualization). • White Cell Morphology: ◦ Döhle bodies: Blue-standing nongranular areas in periphery of cytoplasm; indicate active infection/toxin. ◦ Pelger-Hüet anomaly: Bilobed granulocytes with spectacle-like or 'pince-nez' configuration. ◦ Chédiak-Higashi disease: Giant granules in neutrophil (rare genetic disorder). ◦ Hypersegmented neutrophils: ≥ 5 segmented nuclear lobes; indicates megaloblastic anemia. • Platelet Findings: ◦ Large/Giant: Associated with myeloproliferative disorders. ◦ Clumping: Artifact of anticoagulant. ◦ Granule Absence: Gray platelet syndrome or handling artifact. • Aggregation Findings: ◦ Rouleaux formation: Red cells in stacks; indicates increased serum protein levels. ◦ Red cell agglutination: Irregular collections; may be artifact or indicate antibodies.

DIFFERENTIAL DIAGNOSIS

• Microcytic Anemia Differential: ◦ Iron Deficiency: Small red cells, hypochromic, large RDW (15–18%), high size variability. ◦ Thalassemia: Small red cells of uniform size, normal RDW (11–14%), low size variability. ◦ Dimorphic Anemia: Large RDW; seen in conditions like chronic atrophic gastritis (B12 malabsorption + blood loss). • Poikilocytosis Differential: ◦ Spherocytes: Hereditary spherocytosis, other hemolytic anemias, clostridial sepsis. ◦ Dacrocytes: Hemolytic anemias, severe iron deficiency, thalassemias, myelofibrosis, MDS. ◦ Schistocytes: Microangiopathic hemolytic anemia (MAHA), mechanical fragmentation (heart valve). ◦ Echinocytes: Artifact of drying/storage; renal failure, malnutrition. ◦ Acanthocytes: Renal disease, abetalipoproteinemia, splenectomy, McLeod blood group. ◦ Elliptocytes: Inhered membrane defect, iron deficiency, MDS, megaloblastic anemia, thalassemias. ◦ Stomatocytes: Inherited membrane defect, alcoholism, artifact of dehydration. • Target Cell Differential: ◦ Thalassemia (classic), iron deficiency, cholestatic liver disease, hemoglobinopathies, HbC disease, artifact. • White Cell Morphology Differential: ◦ Pelger-Hüet anomaly: Benign disorder; bilobed granulocytes with spectacle-like/pince-nez configuration. ◦ Döhle bodies: Infections, toxic states (rough ER aggregates). ◦ Chédiak-Higashi disease: Giant granules in neutrophil (rare genetic disorder). • Platelet Differential: ◦ Large/Giant Platelets: Rapid turnover, myeloproliferative disorders (primary thrombocythemia). ◦ Clumping: Artifact of anticoagulant. ◦ Granule Absence: Gray platelet syndrome or handling artifact.

INVESTIGATIONS & DIAGNOSIS

• Diagnostic Approach for Red Cell Morphology: 1. Request Wright-stained peripheral blood smear. 2. Examine at feathered edge (single layer). 3. Use oil immersion lens (100x magnification). 4. Identify size: Compare to small lymphocyte nucleus (8 μm). 5. Identify shape: Look for spherocytes, schistocytes, etc. 6. Identify inclusions: Basophilic stippling, Howell-Jolly bodies, Heinz bodies. • Platelet Count Assessment: 1. Identify platelets in 5–6 fields. 2. Average number per field. 3. Multiply by 20,000 to estimate count. 4. Compare with automated count; if discrepancy exists, check for clumping or fragmentation. • RDW Interpretation: 1. Calculate RDW: (standard deviation of MCV / mean MCV) imes 100. 2. Normal Range: 11–14%. 3. Elevated Range: 15–18% (indicates morphologic anisocytosis). 4. Clinical Logic: - Microcytic anemia + Normal RDW → Thalassemia. - Microcytic anemia + High RDW → Iron deficiency. - Dimorphy/High RDW → Suggests mixed etiology (e.g., B12 malabsorption + blood loss).

MANAGEMENT & TREATMENT

• Step 1: Initial Assessment ◦ Request Wright-stained peripheral blood smear. ◦ Identify optimal viewing area (feathered edge). • Step 2: Quantitative Analysis ◦ Perform manual platelet count to verify automated results if discrepancy exists. ◦ Assess RDW for differentiation of microcytic anemias. • Step 3: Qualitative Interpretation ◦ Evaluate red cell size, shape, and inclusions. ◦ Identify white cell morphology (Döhle bodies, Pelger-Hüet, Chédiak-Higashi). • Step 4: Clinical Correlation ◦ Correlate findings with patient history (e.g., lead exposure for stippling, splenectomy for Howell-Jolly). ◦ Refer to hematology if myeloproliferative features (giant platelets) or severe hemolysis (schistocytes) are present.

KEY PEARLS & CLINICAL TRAPS

• Rule of Thumb: Use the small lymphocyte nucleus as a constant size reference for red cells. ◦ Normal diameter ≈ 8 μm. • RDW Utility: High RDW in microcytic anemia is a key differentiator between iron deficiency and thalassemia. • Platelet Clumping: Always check for clumping if automated counts are unexpectedly low; often caused by anticoagulant. • Döhle Bodies: These represent rough endoplasmic reticulum; their presence indicates active infection or toxic states. • Pelger-Hüet: A benign finding, but can be associated with myelodysplastic syndromes (MDS). • Spherocytes vs. Schistocytes: Spherocytes indicate membrane issues/hemolysis; schistocytes indicate mechanical fragmentation.