Elevated Eosinophils and Platelets in Uncontrolled Asthma
Yes, elevated eosinophils are a direct consequence of uncontrolled asthma, but elevated platelets are not typically associated with asthma control status.
Eosinophils in Uncontrolled Asthma
Eosinophilic inflammation is strongly associated with poorly controlled asthma and predicts future exacerbations. The relationship is well-established through multiple lines of evidence:
Blood Eosinophil Elevation
- Blood eosinophil counts ≥400 cells/μL are an independent risk factor for future asthma exacerbations in patients with severe uncontrolled asthma, with a 1.55-fold increased risk of experiencing 2 or more exacerbations and a 2.29-fold increased risk of emergency department visits or hospitalizations 1
- Patients with persistent asthma and blood eosinophil counts ≥400 cells/mm³ demonstrate a 31% increased rate of future asthma exacerbations compared to those with lower counts 2
- Higher blood eosinophil counts are associated with more frequent asthma attacks, particularly in children, with this association holding across multiple cutoff points (200,300, or 400 cells/μL) 3
Sputum Eosinophil Elevation
- Sputum eosinophils are significantly higher in patients with poorly controlled asthma compared to those with controlled asthma, regardless of asthma severity 4
- The upper limit of normal for sputum eosinophil differential count is 1.9%, and eosinophilic airway inflammation is defined as counts >1.9% 5
- A raised sputum eosinophil count predicts asthma exacerbations with 90% sensitivity when inhaled corticosteroids are withdrawn, and management strategies targeting eosinophil normalization reduce severe exacerbations by up to 60% 5
Mechanism in Uncontrolled Disease
- Uncontrolled and refractory asthma demonstrate persistent Th2-predominant inflammation with eosinophils and lymphocytes present in large quantities, along with elevated Th2-type cytokines such as IL-4 and IL-5 6
- In steroid-resistant asthma, eosinophils and Th2 cytokines remain elevated and do not decrease with corticosteroid therapy, suggesting persistent eosinophilic inflammation despite treatment 6
- Type 2 asthma is characterized by high blood eosinophils (≥150 cells/μL) and frequent exacerbations 6
Clinical Utility of Eosinophil Monitoring
- Blood eosinophil percentage ≥2.7% predicts eosinophilic asthma with 92.2% sensitivity and 75.8% specificity in uncontrolled asthma 7
- An absolute blood eosinophil count ≥0.26 × 10⁹/L is highly predictive of eosinophilic asthma with an area under the curve of 0.898 7
- Eosinophil counts respond rapidly to corticosteroids (potentially as early as 6 hours), with 2- to 7-fold reductions following treatment 5
Platelets in Uncontrolled Asthma
There is no evidence in the provided guidelines or research linking elevated platelet counts to uncontrolled asthma. The available evidence focuses exclusively on eosinophils, neutrophils, and lymphocytes as the relevant inflammatory cells in asthma pathophysiology 6.
If platelets are elevated in a patient with uncontrolled asthma, alternative explanations should be investigated, including:
- Reactive thrombocytosis from chronic inflammation (non-specific)
- Concurrent infection or inflammatory conditions unrelated to asthma
- Medication effects (particularly systemic corticosteroids, which can cause mild thrombocytosis)
- Hematologic disorders requiring separate evaluation
Key Clinical Pitfalls
- Peripheral blood eosinophil counts may not correlate with tissue eosinophilia, particularly in conditions like eosinophilic esophagitis where tissue biopsy remains the gold standard 8
- Timing of eosinophil measurement relative to corticosteroid treatment is critical, as counts decrease rapidly with therapy 5
- Some patients with refractory asthma demonstrate neutrophilic rather than eosinophilic inflammation, which is less responsive to corticosteroids and may represent a different inflammatory phenotype 6
- Age may affect blood eosinophil counts, particularly over age 50 5