What will a Complete Blood Count (CBC) reveal in a patient with leukemia?

CBC Findings in Leukemia

A Complete Blood Count (CBC) in leukemia typically reveals leukocytosis with abnormal white blood cell differential, often accompanied by anemia and thrombocytopenia, though the specific pattern varies significantly by leukemia subtype.

Acute Myeloid Leukemia (AML)

Initial CBC Findings

• Leukocytosis with circulating blasts is common, though white blood cell counts can be variable 1
• Anemia (hemoglobin <11.0 g/dL) is frequently present 1
• Thrombocytopenia (platelets <100,000/μL) occurs in most cases 1
• Neutropenia may be present despite elevated total WBC due to replacement by blasts 1
• Up to 18% of AML patients present with hyperleukocytosis (WBC >100,000/μL), which carries risk of leukostasis and requires urgent cytoreduction 2

Differential Count Characteristics

• Peripheral blood blasts are typically visible, with percentage varying by disease burden 1
• The presence of Auer rods in blasts is pathognomonic for AML 1
• Absolute neutrophil count is often decreased despite high total WBC 1

Chronic Myeloid Leukemia (CML)

Chronic Phase Presentation

• Marked leukocytosis with high differentiated granulocyte counts is characteristic 1
• "Pathological left shift" showing granulocytic precursor cells (myelocytes, metamyelocytes, promyelocytes) in peripheral blood 1
• Mild anemia is common 1
• Normal or elevated platelet counts distinguish CML-CP from acute leukemias 1
• Basophilia may be present and is a criterion for accelerated phase when ≥20% 1
• Blasts are typically <10% in chronic phase 1

Advanced Phase Indicators

• Blast percentage 10-19% indicates accelerated phase (by ICC criteria) 1
• Blast percentage ≥20-30% defines blast phase (criteria vary by classification system) 1, 3
• Thrombocytopenia (<100,000/μL) unrelated to therapy suggests accelerated phase 1

Chronic Lymphocytic Leukemia (CLL)

Diagnostic CBC Criteria

• Sustained lymphocytosis ≥5,000/μL (5 × 10⁹/L) is required for diagnosis 1, 4, 5
• Small, morphologically mature lymphocytes predominate on blood smear 4, 5
• Unlike acute leukemias, even markedly elevated WBC counts rarely cause leukostasis symptoms 1, 4, 5

Associated Cytopenias

• Anemia (hemoglobin <11.0 g/dL) develops with disease progression 1, 5
• Thrombocytopenia (platelets <100,000/μL) indicates advanced disease 1, 5
• Progressive marrow failure with worsening cytopenias is an indication for treatment 5

Important Caveat

• The absolute lymphocyte count alone should never be used as the sole treatment indicator, regardless of how elevated 1, 4, 5
• Treatment decisions require assessment of disease-related symptoms, lymphocyte doubling time (<6 months), and progressive marrow failure 4, 5

Acute Lymphoblastic Leukemia (ALL)

CBC Pattern

• Variable WBC count ranging from leukopenia to marked leukocytosis 6
• Circulating lymphoblasts are typically present 6
• Anemia and thrombocytopenia are common at presentation 6
• More frequent in children than adults 6

General Principles Across All Leukemias

Common CBC Abnormalities

• Leukocytosis is the most consistent finding, though not universal 6, 7
• Abnormally elevated or depressed cell lines beyond just WBC are typical 6
• Nonspecific findings require bone marrow examination or peripheral blood flow cytometry for definitive diagnosis 1, 6

Critical Action Points

• Any patient with suspected leukemia based on CBC should be referred promptly to hematology-oncology 6
• Hyperleukocytosis (WBC >100,000/μL) requires urgent evaluation for leukostasis, tumor lysis syndrome, and DIC 2
• CBC alone cannot distinguish leukemia subtypes—immunophenotyping, cytogenetics, and molecular studies are essential 1

Monitoring Requirements

• Daily CBC with differential during induction chemotherapy for acute leukemias 1
• Every 15 days until complete hematologic response in CML 1
• Every 3-6 months for asymptomatic CLL patients on watch-and-wait 4, 5