Peripheral Blood Smear Interpretation - 2nd MBBS Pathology Practical

CASE H5 - Acute Lymphoblastic Leukemia (ALL)

CBC Analysis

Peripheral Smear Findings

• RBCs: Microcytes, hypochromia, poikilocytes, anisocytes
• WBCs: Blasts with high N:C ratio, scanty agranular cytoplasm (key feature - absence of granules distinguishes lymphoblasts from myeloblasts)
• Platelets: Reduced

Interpretation

1. 95% lymphoblasts in the differential - this alone is diagnostic
2. Blasts have agranular cytoplasm - hallmark of lymphoid lineage
3. Pancytopenia (anemia + thrombocytopenia + neutropenia) due to bone marrow replacement by blasts
4. Leukocytosis is paradoxical - WBC count is very high but functional cells are absent (it is a "leukemic" count of non-functional blasts)
5. Splenomegaly + jaundice - due to extramedullary hematopoiesis and hemolysis
6. Age 14 years - ALL has a bimodal peak; childhood peak (2-10 years, this is slightly older but still pediatric)
7. Normoblasts (nucleated RBCs) in peripheral blood = leukoerythroblastic reaction due to marrow stress

"The peripheral blood smear shows marked leukocytosis (1,20,000/mm³) with 95% lymphoblasts having a high N:C ratio and agranular cytoplasm. There is associated anemia (Hb 8 g/dL), thrombocytopenia (50,000/mm³), and the presence of normoblasts (3/100 WBC). These findings, in the clinical context of a 14-year-old boy with short stature, icterus, and splenomegaly, are consistent with Acute Lymphoblastic Leukemia (ALL)."

CASE H8 - Acute Myeloid Leukemia (AML)

CBC Analysis

Peripheral Smear Findings

• RBCs: Microcytes (++), hypochromia (+++), anisocytes (++)
• WBCs: Blasts with high N:C ratio, scanty granular cytoplasm (Auer rods may be present - not mentioned here but characteristic)
• Platelets: Reduced

Interpretation

1. 85% myeloblasts - WHO criterion for AML is ≥20% blasts in bone marrow; 85% is far above threshold
2. Blasts have granular cytoplasm - this distinguishes myeloblasts from lymphoblasts
3. The presence of a "leukemic hiatus" - myeloblasts (85%) present alongside mature neutrophils (5%), with intermediate stages (promyelocytes, myelocytes) at very low percentages; this gap between immature and mature forms is the leukemic hiatus
4. Pancytopenia - bone marrow replaced by blasts, causing functional failure
5. Bone pain - due to marrow infiltration by blasts expanding the medullary cavity
6. Frequent infections - functional neutropenia despite high WBC count
7. Easy bruising - thrombocytopenia (50,000/mm³)
8. Age 60 - AML is predominantly a disease of older adults (median age ~68 years)

"The peripheral blood smear shows marked leukocytosis (2,20,000/mm³) with 85% myeloblasts having a high N:C ratio and granular (scanty) cytoplasm. A leukemic hiatus is noted. There is associated normocytic normochromic anemia (Hb 8 g/dL) and thrombocytopenia (50,000/mm³). In the clinical context of a 60-year-old male presenting with bone pain, frequent infections, pallor, and easy bruising, these findings are consistent with Acute Myeloid Leukemia (AML)."

CASE H6 - Chronic Myeloid Leukemia (CML)

CBC Analysis

Peripheral Smear Findings

• RBCs: Microcytes, macrocytes, hypochromia, poikilocytes, anisocytes (dimorphic picture)
• WBCs: "Shift to left" - full myeloid maturation series present (blast → promyelocyte → myelocyte → metamyelocyte → band → neutrophil)
• Platelets: Increased

Interpretation

1. Extreme leukocytosis (5,00,000/mm³) with the entire myeloid maturation spectrum visible = "myeloid spectrum" or shift to the left
2. Myelocyte peak at 30% - in CML, myelocytes predominate among immature forms (unlike AML where blasts predominate)
3. Basophilia (10%) - absolute basophilia is a hallmark of CML and helps distinguish it from a leukemoid reaction
4. Eosinophilia (8%) - also characteristically elevated in CML
5. Thrombocytosis (5,00,000) - elevated platelets are typical in CML (contrast with AML/ALL where platelets are low)
6. Blasts only 2% - low blast count distinguishes CML chronic phase from blast crisis (blast crisis = ≥20% blasts)
7. Massive splenomegaly - the most striking clinical feature of CML; due to extramedullary hematopoiesis
8. Philadelphia chromosome (BCR-ABL) - the underlying cytogenetic abnormality (t9;22) causing constitutive tyrosine kinase activity; not seen on smear but essential to mention in exam
9. NO leukemic hiatus - unlike AML, CML shows the complete maturation spectrum without a gap

"The peripheral blood smear shows extreme leukocytosis (5,00,000/mm³) with a complete left shift showing the entire myeloid maturation series. Basophilia (10%) and eosinophilia (8%) are prominent. Platelets are increased (5,00,000/mm³). RBCs show microcytes, hypochromia, and anisocytosis. In the clinical context of a 50-year-old female with massive splenomegaly, these findings are consistent with Chronic Myeloid Leukemia (CML). The diagnosis should be confirmed by demonstration of the Philadelphia chromosome (BCR-ABL1 fusion gene) on cytogenetics/FISH."

Comparative Summary Table (for exam quick revision)

Important Distinguishing Points for Viva

• ALL blasts: agranular cytoplasm, round nuclei, no Auer rods
• AML blasts: granular cytoplasm, Auer rods (pathognomonic of AML), MPO positive

• CML: basophilia present, LAP (Leukocyte Alkaline Phosphatase) score LOW, Philadelphia chromosome positive
• Leukemoid reaction: basophilia absent, LAP score HIGH, no Philadelphia chromosome

• Acute: predominantly blasts (≥20%), rapid onset, short survival if untreated
• Chronic: mature cells with left shift, slow onset, better prognosis initially