Leukopenia Work-Up
Begin with a complete blood count (CBC) with differential and peripheral blood smear to determine the absolute neutrophil count (ANC) and identify which white blood cell lineage is reduced, as this guides all subsequent diagnostic decisions. 1, 2, 3
Initial Laboratory Assessment
Essential First-Line Tests
- CBC with differential: Determine if leukopenia is isolated or part of bi/pancytopenia, which suggests bone marrow production failure rather than peripheral destruction 3, 4
- Peripheral blood smear with manual differential: Critical for identifying dysplasia, abnormal cell morphology, and accurate cell counts that automated analyzers may miss 1, 2, 3
- Absolute neutrophil count (ANC): Calculate to classify severity—neutropenia is defined as ANC <1,500/mcL, with severe neutropenia at <500/mcL carrying highest infection risk 4
- Reticulocyte count: Helps distinguish production versus destruction causes 5
Determine Chronicity and Context
- Review previous blood counts: Essential to determine if leukopenia is acute versus chronic, as this fundamentally changes the differential diagnosis 3
- Medication review: Identify drugs causing leukopenia (chemotherapy, antibiotics including cephalosporins, antithyroid drugs, anticonvulsants, immunosuppressants) 6, 4, 7
- Infection history: Viral infections (HIV, EBV, CMV, hepatitis) commonly cause transient leukopenia 6, 4
Secondary Testing Based on Initial Findings
If Isolated Neutropenia Without Other Cytopenias
- Vitamin B12 and folate levels: Megaloblastic changes can cause leukopenia 5, 6
- Viral studies: HIV, hepatitis panel, EBV, CMV if clinically indicated 1, 6
- Autoimmune workup: ANA, rheumatoid factor if systemic symptoms suggest autoimmune neutropenia 6, 4
- Thyroid function tests: Hypothyroidism can cause cytopenias 5
If Bi/Pancytopenia Present
Proceed directly to bone marrow evaluation, as this indicates bone marrow production failure requiring morphologic assessment. 1, 3
Bone Marrow Evaluation Indications
Bone marrow aspiration and biopsy are indicated for: 1, 2
- Persistent unexplained leukopenia despite initial workup
- Any bi- or pancytopenia (suggests marrow failure)
- Presence of dysplastic cells on peripheral smear
- Concern for hematologic malignancy (blasts, lymphocytosis with abnormal morphology)
Comprehensive Bone Marrow Studies
When bone marrow is performed, obtain: 1, 2
- Morphologic evaluation: Aspirate smears and core biopsy with touch preparations
- Flow cytometry immunophenotyping: Panel sufficient to distinguish AML, ALL, lymphoproliferative disorders, and ambiguous lineage leukemias
- Conventional cytogenetic analysis (karyotype): Cannot be replaced by FISH or molecular testing alone
- Molecular genetic testing: Guided by clinical suspicion (FLT3-ITD, NPM1, CEBPA for suspected AML)
- FISH studies: For specific chromosomal abnormalities when indicated
Critical pitfall: Never start chemotherapy or definitive treatment before obtaining adequate bone marrow material for all diagnostic studies, as this may obscure the diagnosis permanently. 2
Urgent Management Considerations
Febrile Neutropenia (ANC <500/mcL with fever ≥38.3°C)
This is a medical emergency requiring immediate hospital admission and broad-spectrum antibiotics within 1 hour to reduce mortality. 3, 4
- Obtain blood cultures before antibiotics but do not delay treatment
- Start empiric broad-spectrum coverage (antipseudomonal beta-lactam)
- Consider G-CSF if prolonged severe neutropenia expected 8
Risk Stratification
The major danger of neutropenia is infection risk, which correlates with: 6, 4
- Severity: ANC <500/mcL = high risk, <100/mcL = very high risk
- Duration: Prolonged neutropenia (>7 days) increases infection risk exponentially
- Clinical status: Fever, mucositis, indwelling catheters increase risk
Common Etiologies to Consider
Most Common Causes 6, 4
- Medications: Most common reversible cause in outpatient setting
- Viral infections: Usually transient, self-limited
- Autoimmune disorders: Can cause chronic neutropenia
- Nutritional deficiencies: B12/folate causing megaloblastic changes
- Hematologic malignancies: Leukemia, lymphoma, myelodysplastic syndrome
- Hypersplenism: Check for splenomegaly on exam
Special Populations
- Chronic benign ethnic neutropenia: Common in individuals of African, Middle Eastern, or West Indian descent—baseline ANC 1,000-1,500/mcL without increased infection risk 4
- Hereditary neutropenia: Rare, usually presents in childhood with recurrent infections 6
Sample Handling
Store bone marrow and blood samples appropriately for potential future molecular or genetic studies to ensure diagnostic opportunities are not missed. 1