Eosinophilic Asthma Blood Eosinophil Threshold
According to the GINA 2025 guideline framework, eosinophilic asthma is defined by a blood eosinophil count of ≥150 cells/μL in adults with adult-onset asthma and frequent exacerbations 1.
Key Diagnostic Criteria
The guideline specifically characterizes eosinophilic asthma as:
- Adult-onset asthma
- High blood eosinophils (≥150 cells/μL)
- Frequent exacerbations
This threshold of ≥150 cells/μL is the absolute blood eosinophil count that defines the eosinophilic phenotype 1.
Clinical Context and Distinction from Type 2 Asthma
It's important to distinguish eosinophilic asthma from the broader category of Type 2 asthma. Type 2 asthma is characterized by type 2 airway inflammation evidenced by high blood eosinophils and/or high FeNO, whereas eosinophilic asthma specifically emphasizes the eosinophil component with the clinical pattern of adult onset and frequent exacerbations 1.
Evidence Supporting the 150 cells/μL Threshold
The 150 cells/μL cutoff is well-supported by research evidence:
- Predictive value for anti-eosinophil therapies: Single measurements ≥150 cells/μL predict response to anti-eosinophil biologics like benralizumab and mepolizumab 2, 3
- Stability over time: 85% of patients with baseline counts ≥150 cells/μL maintain this level on average over the following year 3
- Exacerbation risk: Blood eosinophil counts ≥150 cells/μL are associated with increased future exacerbation rates and poorer asthma control 4, 5
Important Clinical Caveats
Single measurements may be inadequate in some cases: Research shows that 65% of patients with severe asthma shift between eosinophil count groups over time, with most shifts occurring by week 24 2. Patients with initially low counts (<150 cells/μL) are particularly prone to shifting groups, with 59% shifting by week 4 2.
When to repeat measurements: If a patient presents with a low eosinophil count but has clinical features suggesting eosinophilic disease (adult-onset, frequent exacerbations, nasal polyps), consider repeat measurements as the count may be intermittently low rather than consistently low 6. Patients with variable counts experience similar exacerbation rates to those with consistently high counts 6.