Allergy Testing in Non-Eosinophilic Asthma
Allergy testing has minimal to no role in adults with poorly controlled non-eosinophilic asthma, as this phenotype is not driven by allergic mechanisms and will not respond to allergen-directed interventions.
Understanding Non-Eosinophilic Asthma
Non-eosinophilic (non-type 2) asthma is characterized by the absence of high blood eosinophils and high FeNO after ruling out other chronic obstructive airway diseases 1. This phenotype fundamentally differs from allergic asthma, which is defined as asthma associated with sensitization to aeroallergens leading to symptoms and airway inflammation 2.
The key distinction: Your patient's non-eosinophilic phenotype indicates their asthma is not driven by the TH2 inflammatory pathway that characterizes allergic disease 2.
Why Allergy Testing Is Not Indicated
Mechanistic Mismatch
- Non-eosinophilic asthma lacks the TH2-driven inflammatory process that would respond to allergen identification and avoidance 2
- Biomarkers that distinguish allergic asthma (serum IgE, specific IgE, blood/sputum eosinophils, FeNO) are absent or low in non-eosinophilic phenotypes 2
- FENO levels less than 25 ppb are inconsistent with type 2 inflammation and suggest non-eosinophilic asthma 1
Limited Clinical Utility
- A positive allergy test indicates only sensitization, not clinical allergy or causation of symptoms 3
- Allergy testing should only be performed when identification of a specific allergen would change management 4
- In non-eosinophilic asthma, allergen avoidance strategies will not improve asthma control since the disease mechanism is not allergen-driven 5
When Allergy Testing Might Be Considered
Allergy testing is specifically recommended for asthma patients who:
- Have frequent exacerbations, emergency visits, or hospitalizations 6
- Require oral corticosteroids or high-dose inhaled steroids 6
- Are candidates for advanced therapies like biologics or allergen immunotherapy 6
Critical caveat: These recommendations apply to patients with eosinophilic or type 2 asthma, not your non-eosinophilic patient 1, 6.
What to Do Instead
Focus on Non-Allergic Triggers
- Identify non-allergic triggers: infections, irritants, exercise, cold air, stress 1
- Optimize inhaled corticosteroid and bronchodilator therapy 1
- Assess for comorbidities: GERD, obesity, obstructive sleep apnea, vocal cord dysfunction 1
Ensure Accurate Phenotyping
- Confirm blood eosinophil count is consistently <150 cells/μL 1
- Verify FeNO is <25 ppb (or <20 ppb if measured when younger) 1
- Rule out poor adherence to inhaled corticosteroids as a cause of poor control 1
Common Pitfalls to Avoid
Do not order allergy testing reflexively for all poorly controlled asthma - the phenotype determines whether testing will provide actionable information 6, 3.
Do not pursue allergen immunotherapy - this is contraindicated in poorly controlled asthma regardless of phenotype, and offers no benefit in non-eosinophilic disease 1, 2.
Do not assume sensitization equals causation - even if incidental positive allergy tests are found, they do not explain non-eosinophilic asthma pathophysiology 3.