CBC Findings in Leukemia
The CBC in leukemia typically shows abnormal white blood cell counts (either markedly elevated or decreased), presence of immature cells (blasts), and often cytopenias in one or more cell lines, with specific patterns varying by leukemia type.
Chronic Myeloid Leukemia (CML)
Chronic Phase Presentation
- Leukocytosis with left shift: WBC counts frequently exceed 100 × 10⁹/L, with immature granulocytes ranging from metamyelocytes to myeloblasts visible in the differential 1
- Basophilia: Common finding that helps distinguish CML from reactive leukocytosis; absolute basophil count ≥200/mm³ is characteristic 1, 2
- Thrombocytosis: Elevated platelet counts are frequently present at diagnosis 1
- Blast percentage: Less than 15% blasts in blood and bone marrow defines chronic phase 1
- Eosinophilia: May be prominent in some cases 1
- Anemia: Mild anemia is common at presentation 1
Preleukemic CML
- Normal to mildly elevated WBC: Can present with WBC as low as 3.6-14.3 K/mm³ with 50-73% granulocytes and 0% blasts 2
- Absolute basophilia: Present in only 4 of 7 cases (≥200/mm³), making this a less reliable early marker 2
Accelerated/Blast Phase
- Accelerated phase: 15-29% blasts in blood or bone marrow, >20% basophils, or thrombocytosis/thrombocytopenia unrelated to therapy 1
- Blast phase: ≥30% blasts in blood or bone marrow 1
Acute Myeloid Leukemia (AML)
Diagnostic Criteria
- Blast percentage: ≥20% blasts in marrow or peripheral blood establishes the diagnosis 1
- Exception for specific cytogenetics: Diagnosis can be made with <20% blasts if recurrent cytogenetic abnormalities are present, including t(15;17), t(8;21), t(16;16), or inv(16) 1
Hyperleukocytosis
- Extreme leukocytosis: WBC >100,000 cells/mm³ occurs in 5-30% of adult patients with acute leukemias 3, 4
- Medical emergency: Associated with leukostasis, requiring prompt recognition to prevent respiratory failure or intracranial hemorrhage 3, 4
- Risk factors: Younger age, myelomonocytic or monocytic morphology, and certain cytogenetic abnormalities increase risk 4
Chronic Lymphocytic Leukemia (CLL)
Typical Findings
- Lymphocytosis: Clonal accumulation of mature-appearing lymphocytes in peripheral blood 1, 5
- Prognostic markers in CBC:
Response Criteria
- Complete remission requires: Hemoglobin >11.0 g/dL, platelets >100,000/μL, neutrophils >1,500/μL, and lymphocytes <4,000/μL 1
Pediatric CML Considerations
Characteristic Features
- High leukocyte counts: Unregulated growth of myeloid cells with pathological left shift 1
- Mild anemia: Common at presentation 1
- Normal or elevated platelets: Typical finding in chronic phase 1
- Bleeding signs: Present in 20% of children at diagnosis despite normal/elevated platelet counts (likely due to platelet dysfunction) 1
Key Monitoring Recommendations
Surveillance Frequency
- High-risk conditions: CBC every 3-4 months even with stable counts for highest-risk diseases like Fanconi anemia 1, 6
- New cytopenia: Repeat CBC within 2-4 weeks if patient develops cytopenia of one or more lineages 1, 6
- Worsening counts: If CBC worsens or remains abnormal over two or more measurements, proceed to bone marrow evaluation 1, 6
Common Pitfalls to Avoid
- Missing preleukemic CML: Don't dismiss normal or mildly elevated WBC counts in the presence of absolute basophilia; consider cytogenetic testing 2
- Overlooking hyperleukocytosis urgency: WBC >100,000/mm³ requires immediate intervention regardless of patient symptoms to prevent leukostasis complications 3, 4
- Relying solely on blast percentage: In CML, the presence of basophilia, left shift, and characteristic cytogenetics are equally important diagnostic features 1
- Ignoring platelet dysfunction: Normal or elevated platelet counts don't exclude bleeding risk in leukemia; functional abnormalities are common 1