White Blood Cell Appearance in Leukemia
In leukemia, WBCs typically appear as abnormal cells with specific morphologic features depending on the type: chronic lymphocytic leukemia shows small, mature lymphocytes with narrow cytoplasm and dense nuclei; chronic myeloid leukemia displays increased myeloid cells in all maturation stages with predominance of mature forms; and acute leukemias present with increased immature blast cells (≥20% blasts defining blast phase). 1
Chronic Lymphocytic Leukemia (CLL)
Morphologic Features
- Small, mature-appearing lymphocytes with a narrow border of cytoplasm and dense nucleus lacking discernible nucleoli, with partially aggregated chromatin 1
- Gumprecht nuclear shadows (smudge cells) found as cell debris are characteristic morphologic features 1
- May be admixed with larger or atypical cells, cleaved cells, or prolymphocytes (up to 55% of blood lymphocytes) 1
- Requires at least 5,000 clonal B lymphocytes/μL (5 × 10^9/L) in peripheral blood for diagnosis 1, 2
Immunophenotype
- CLL cells coexpress CD5 (T-cell antigen) with B-cell markers CD19, CD20, and CD23 1
- Characteristically low levels of surface immunoglobulin, CD20, and CD79b compared to normal B cells 1
- Each clone restricted to either kappa or lambda light chain expression 1
Chronic Myeloid Leukemia (CML)
Bone Marrow and Blood Findings
- Increased cellularity due to proliferation of myelopoiesis in all stages of maturation with predominance of mature forms 1
- Basophilia is common, and eosinophils may be prominent 1
- In chronic phase: <15% blasts in blood and bone marrow 1
- Megakaryocytes are smaller than normal with hypolobulated nuclei 1
Peripheral Blood Characteristics
- WBC count often exceeding 100 × 10^9/L 1
- Presence of immature granulocytes (metamyelocytes, myelocytes, promyelocytes) with few or occasional myeloblasts 1
- Peripheral blood absolute basophilia (≥200/mm³) is a distinguishing feature 3
Disease Progression Markers
- Accelerated phase: 15-29% blasts (ELN criteria) or 10-19% blasts (WHO criteria) 1
- Blast phase: ≥30% blasts (ELN criteria) or ≥20% blasts (WHO criteria) 1
- Distinction between myeloid (70-80%) and lymphoid (20-30%) blast crisis requires immunocytology by flow cytometry 1
Acute Leukemias
Blast Cell Characteristics
- At least 20% immature forms/blasts defines acute leukemia 1
- Myeloid leukemia without maturation shows many immature forms/blasts with azurophilic granules 1
- Myeloid leukemia with maturation displays heterogeneous differentiation with ring forms 1
Red Blood Cell Changes
Associated RBC Morphology
- Acute myeloid leukemia (AML): presence of large central holes in RBCs 4
- Acute lymphoblastic leukemia (ALL) and CML: thorn- and horn-like structures in RBCs 4
- CLL: flaccid appearance of RBCs 4
- These alterations represent pathophysiological signatures of anemia associated with leukemia 4
Clinical Pitfalls and Important Caveats
Diagnostic Considerations
- Flow cytometry is essential to confirm clonality of circulating B lymphocytes in CLL 1
- Distinguish CLL from other lymphoproliferative disorders: mantle cell lymphoma (CD5+/CD23-), B-cell prolymphocytic leukemia (high CD20/surface Ig, 50% lack CD5) 1
- In CML, pre-leukemic phase may present with normal or mildly elevated WBC (3.6-14.3 K/mm³) but still shows BCR-ABL1 fusion 3
Treatment Decision Points
- Elevated WBC count alone is NOT an indication for treatment in CLL 2
- Treatment should be based on disease-related symptoms, progressive disease, or lymphocyte doubling time <6 months 2
- Unlike acute leukemias, even markedly elevated WBC counts in CLL rarely cause leukostatic symptoms 2