Guideline Summary for Diagnosis of Non‑Asthmatic Eosinophilic Bronchitis
Diagnostic Criteria
A diagnosis requires chronic cough lasting ≥8 weeks, normal spirometry (no variable airflow obstruction), normal airway hyperresponsiveness (methacholine PC₂₀ > 16 mg/mL), and induced sputum eosinophilia ≥3 % of non‑squamous cells. The combination of these four elements defines the condition. 1, 2, 3, 4, 5
Chronic cough definition: cough persisting for at least eight weeks. 3
Normal spirometry: FEV₁/FVC ratio within predicted limits and no significant bronchodilator response, confirming the absence of variable airflow obstruction. 1, 4
Normal airway hyperresponsiveness: methacholine challenge with PC₂₀ > 16 mg/mL excludes cough‑variant asthma. 1, 5
Sputum eosinophilia threshold: ≥3 % eosinophils (normal <1.1 %) on induced sputum is diagnostic. 1, 2
Exclusion of Other Causes of Chronic Cough
Chest radiograph should be performed to rule out structural lung disease, malignancy, or infection before sputum analysis. 2
Spirometry with bronchodilator testing must demonstrate a normal FEV₁/FVC ratio and lack of bronchodilator responsiveness, thereby excluding asthma. 1, 7
Methacholine Challenge Testing
A normal methacholine result (PC₂₀ > 16 mg/mL) supports non‑asthmatic eosinophilic bronchitis. 5
A positive result (PC₂₀ ≤ 16 mg/mL) indicates cough‑variant asthma rather than non‑asthmatic eosinophilic bronchitis. 5
Induced Sputum Analysis (Gold‑Standard Test)
Induced sputum is the preferred diagnostic method; it requires same‑day processing for accurate cell counts. 1
Technique highlights:
Alternative when induction fails: bronchoscopy with bronchial wash fluid yields comparable eosinophil data. 1
Differentiation from Asthma (ACCP Guidelines)
| Feature | Non‑Asthmatic Eosinophilic Bronchitis | Cough‑Variant Asthma | Classic Asthma |
|---|---|---|---|
| Airway hyperresponsiveness | Absent (PC₂₀ > 16 mg/mL) | Present | Present |
| Bronchodilator response | Absent | Good | Good |
| Spirometry | Normal | Normal | Abnormal |
| Sputum eosinophilia | Always present (≥3 %) | Usually present | Usually present |
These distinctions are based on ACCP guideline recommendations. 1, 2, 5
Epidemiology
- Non‑asthmatic eosinophilic bronchitis accounts for 10–30 % of chronic cough cases referred to specialist clinics. 8, 7
Clinical Management Considerations
Response to other treatments: If cough does not improve—or only partially improves—after addressing another identified cause, non‑asthmatic eosinophilic bronchitis should be investigated. 1, 3
Exhaled nitric oxide (FeNO): Although sometimes elevated, FeNO lacks sufficient validation as a standalone diagnostic tool; sputum eosinophil count remains definitive. 1
Cough duration: A 30‑day cough is shorter than the chronic definition; initial management should target acute/sub‑acute etiologies (e.g., post‑viral cough). If cough persists beyond eight weeks, full diagnostic work‑up for non‑asthmatic eosinophilic bronchitis is warranted. 3, 2, 4
Productive cough: The condition often presents with a productive cough, allowing for spontaneous sputum collection, though induced sputum provides more reliable quantification. 1
Occupational/allergen exposure: Assessment of workplace and environmental allergen exposures is recommended, as avoidance may be therapeutic. 1, 2