Airway eosinophilia in children with severe asthma - Predictive values of noninvasive tests

Rationale: Children with severe asthma experience persistent symptoms despite maximal conventional treatment. Fraction of exhaled nitric oxide (FENO) and sputum eosinophils are used as markers of airway inflammation to guide treatment with steroids, but no data are available on how reliable they are in predicting airway eosinophilia assessed bronchoscopically in these children. Objectives: To determine how FENO and sputum eosinophils predict airway eosinophilia measured in both bronchoalveolar lavage (BAL) and endobronchial biopsy. Methods: Twenty-seven children with moderate to severe persistent asthma attempted measurement of FENO and sputum eosinophils, followed by bronchoscopy, BAL, and endobronchial biopsy within 24 h. Main Results: Significant correlations were found between eosinophils in sputum and both BAL eosinophils (n = 20, r = 0.45, p = 0.045) and FENO (n = 23, r = 0.42, p = 0.049). The relationship between FENO and BAL eosinophils was also significant with a stronger correlation (n = 24, r = 0.54, p = 0.006). The positive predictive value (PPV) for increased sputum eosinophil percentage (> 2.5%) to detect elevated eosinophils in BAL (> 1.19%) was 75%; the negative predictive value (NPV) was 63%. All patients with both increased sputum eosinophils and an elevated FENO value (> 23 ppb) had elevated eosinophils in BAL (PPV, 100%); the NPV of these two markers was 65%. Eight of nine patients without any sputum eosinophils had normal subepithelial eosinophil numbers (< 1.2%; NPV, 89%). However, the F`PV of any sputum eosinophils for increased subepithelial eosinophilia was only 36.4%. Conclusions: There was moderate agreement between both FENO and sputum eosinophils and BAL eosinophils. There was good NPV, but only poor PPV for these markers for mucosal eosinophilia.