From the Guidelines
The diagnostic criteria for eosinophilic asthma include elevated blood eosinophil counts, elevated sputum eosinophil levels, and elevated fractional exhaled nitric oxide (FeNO) levels, with patients typically presenting with late-onset asthma and poor response to conventional inhaled corticosteroid therapy. According to the most recent study 1, asthma is characterized by respiratory symptoms that fluctuate over time in frequency and intensity and by variable airflow limitation, and is consistently reported as a major cause of chronic cough. The study also notes that non-invasive inflammatory markers such as blood or sputum eosinophil counts and fractional exhaled nitric oxide (F ENO) can provide additional evidence to support the need for corticosteroid treatment.
Some key features of eosinophilic asthma include:
- Elevated blood eosinophil counts (typically ≥300 cells/μL)
- Elevated sputum eosinophil levels (≥2-3% of total cells)
- Elevated fractional exhaled nitric oxide (FeNO) levels (typically >50 parts per billion)
- Late-onset asthma, often after age 12
- Poor response to conventional inhaled corticosteroid therapy
- Clinical features such as chronic rhinosinusitis, nasal polyps, and more severe asthma symptoms with frequent exacerbations despite adherence to standard treatments
The diagnosis of eosinophilic asthma often requires a combination of these findings, rather than a single test, with bronchoscopy with bronchoalveolar lavage sometimes performed to directly measure airway eosinophilia 1. This phenotype is important to identify as these patients often respond well to targeted biologic therapies such as anti-IL-5 medications (mepolizumab, reslizumab, benralizumab), anti-IL-4/IL-13 (dupilumab), or anti-IgE (omalizumab) treatments.
It's worth noting that an earlier study 1 found that F ENO can support a diagnosis of asthma, but its limitations arise from the heterogeneity of airway inflammation in asthma, and it may not always be associated with increased F ENO. However, the more recent study 1 provides a more comprehensive understanding of the diagnostic criteria for eosinophilic asthma.
From the Research
Diagnostic Criteria for Eosinophilia Asthma
The diagnostic criteria for eosinophilia asthma include:
- Significantly elevated blood or sputum eosinophils and/or fractional exhaled nitric oxide 2
- Peripheral blood eosinophilia, typically ≥500 cells/mm3, by pulmonary symptoms and physical examination findings that are nonspecific, and by radiographic evidence of pulmonary disease 3
- Induced sputum cell count is the gold standard for identifying eosinophilic inflammation in asthma, although several noninvasive biomarkers, including fractional exhaled nitric oxide and periostin, are emerging as potential surrogates 4
- Measurements of sputum eosinophils, blood eosinophils, FeNO, serum IgE, and periostin can be used as biomarkers to diagnose eosinophilic asthma 5
Biomarkers for Eosinophilic Asthma
Biomarkers that can be used to diagnose eosinophilic asthma include:
- Blood eosinophils
- Fractional exhaled nitric oxide (FeNO)
- Serum IgE
- Periostin
- Sputum eosinophils These biomarkers can be used separately or in combination, and their accuracy to detect sputum eosinophilia depends on cut-off values 5
Importance of Accurate Diagnosis
Accurate diagnosis of eosinophilic asthma is essential to identify patients who may benefit from targeted therapies, such as monoclonal antibodies 2. Uncontrolled eosinophilic airway inflammation is associated with reduced response to glucocorticoids and increased risk of severe exacerbations 5.