What is an expected finding in the Complete Blood Count (CBC) of an asthma patient?

Expected CBC Findings in Asthma Patients

Elevated blood eosinophil count is the most common and expected finding in the complete blood count (CBC) of an asthma patient, with levels typically ≥300 cells/μL in patients with eosinophilic asthma. 1, 2

Eosinophilia in Asthma

Prevalence and Significance

• Approximately 40% of patients hospitalized for asthma exacerbation demonstrate blood eosinophilia (≥300 cells/μL) 2
• Eosinophilic inflammation is a hallmark feature of asthma pathophysiology, particularly in type 2 asthma 1
• Blood eosinophil counts serve as a biomarker that can help:
  • Predict response to corticosteroid therapy 1
  • Identify patients who may benefit from targeted biologics 3
  • Assess underlying disease activity 1

Patterns of Blood Eosinophilia

Blood eosinophil counts in asthma patients typically show one of three patterns:

1. Predominantly high (≥300 cells/μL) - seen in approximately 42% of patients
2. Predominantly low (<300 cells/μL) - seen in approximately 31% of patients
3. Variable (fluctuating between high and low) - seen in approximately 27% of patients 4

Important Clinical Considerations

Relationship Between Blood and Airway Eosinophilia

• Blood eosinophilia generally correlates with airway eosinophilia, but this relationship is imperfect 1, 5
• Normal blood eosinophil levels do not exclude airway eosinophilic inflammation, especially in:
  • Patients on high-dose corticosteroid therapy 5
  • Children with severe therapy-resistant asthma 5

Eosinophil Subtypes in Asthma

Recent research has identified different eosinophil subtypes in asthma:

• Asthma patients have a higher proportion of inflammatory eosinophils (iEos; Siglec-8+CD62LloIL-3Rhi) compared to COPD patients and healthy individuals 6
• These inflammatory eosinophils express more IL-5 receptors, which may explain the differential response to anti-IL-5 biologics like mepolizumab 3, 6

Clinical Utility of Eosinophil Counts

• Elevated blood eosinophil counts (≥150 cells/μL) help identify eosinophilic asthma 1
• Blood eosinophil counts can guide treatment decisions:
  • Patients with elevated counts typically respond better to inhaled corticosteroids 1
  • Counts ≥300 cells/μL may indicate candidates for biologic therapies targeting IL-5 pathway 3

Monitoring Considerations

• Blood eosinophil counts should be measured before initiating corticosteroid therapy, as steroids can rapidly reduce counts 1
• Repeated measurements may be necessary due to natural variability in counts 4
• Patients with variable eosinophil counts experience similar exacerbation rates to those with consistently high counts 4

Caveats and Pitfalls

• Blood eosinophil counts may be suppressed by systemic corticosteroids, potentially masking underlying eosinophilic inflammation 1
• Time of day, menstrual cycle, and recent allergen exposure can affect eosinophil counts 1
• A single normal blood eosinophil count should not be used to exclude eosinophilic airway inflammation, particularly in severe asthma 5
• Sputum eosinophil counts may provide a more accurate assessment of airway inflammation than blood counts but are less readily available in clinical practice 1

Blood eosinophilia remains the most consistent and clinically relevant CBC finding in asthma patients, serving as a valuable biomarker for diagnosis, phenotyping, and treatment decisions.