What is the initial lab workup for a patient presenting with neutropenia?

Initial Laboratory Workup for Neutropenia

The initial laboratory workup for a patient presenting with neutropenia should include a complete blood count with differential, blood chemistry profile, blood cultures (at least two sets), and additional cultures based on symptoms, along with appropriate imaging studies such as chest radiography. 1

Definition and Risk Assessment

Neutropenia is defined as an absolute neutrophil count (ANC) below 1500 cells/mm³ and can be classified as:

• Mild: 1000-1500 cells/mm³
• Moderate: 500-1000 cells/mm³
• Severe: <500 cells/mm³ 2

The risk of infection increases with the severity and duration of neutropenia, with profound neutropenia (ANC <100 cells/mm³) carrying the highest risk 1.

Essential Laboratory Tests

First-line Laboratory Evaluation:

• Complete blood count (CBC) with differential to confirm neutropenia and assess severity 1
• Blood chemistry profile including:
  • Serum creatinine and blood urea nitrogen
  • Electrolytes
  • Hepatic transaminase enzymes
  • Total bilirubin 3
• Blood cultures - at least 2 sets, with one set collected from each lumen of a central venous catheter (if present) and from a peripheral vein 3
• Additional cultures from sites of suspected infection based on clinical presentation 3

Imaging Studies:

• Chest radiography for patients with respiratory signs or symptoms 3
• Additional imaging based on clinical presentation 1

Additional Workup Based on Clinical Context

For persistent or severe neutropenia, additional testing may include:

• Bone marrow examination with cytogenetics to evaluate for underlying hematologic disorders 4
• Neutrophil antibody testing in the context of clinical and bone marrow findings 4
• Genetic testing for suspected congenital neutropenias 4

Risk Stratification for Febrile Neutropenia

For patients who develop fever with neutropenia, risk stratification is essential using:

• MASCC score (Multinational Association for Supportive Care in Cancer)

  • Score ≥21: low risk
  • Score <21: high risk 1

• Clinical criteria for high-risk patients:

  • Profound neutropenia (ANC <100 cells/mm³) expected to last >7 days
  • Hemodynamic instability
  • Oral/gastrointestinal mucositis interfering with swallowing or causing severe diarrhea
  • Neurologic or mental status changes
  • Catheter-related infection
  • New pulmonary infiltrate or hypoxemia
  • Hepatic or renal insufficiency 3

Common Pitfalls to Avoid

• Delaying laboratory evaluation in patients with severe neutropenia
• Failing to obtain adequate blood cultures before initiating antibiotics
• Not considering the underlying cause of neutropenia, which guides further management
• Overlooking signs of infection in neutropenic patients, as inflammatory responses may be blunted 1

Algorithm for Neutropenia Workup

1. Confirm neutropenia with CBC and differential
2. Assess severity based on ANC level
3. Evaluate for infection with blood cultures and targeted cultures based on symptoms
4. Perform appropriate imaging based on clinical presentation
5. Consider bone marrow examination for persistent, severe, or unexplained neutropenia
6. Initiate empiric antibiotics for febrile neutropenia without delay

For patients with suspected chronic neutropenia, confirming the diagnosis through serial CBCs with differentials and bone marrow examination is essential before initiating treatments such as G-CSF 5.