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 (Fe(NO)) 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 Fe(NO) 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 Fe(NO) 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 Fe(NO) (n = 23, r = 0.42, p = 0.049). The relationship between Fe(NO) 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 Fe(NO) 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 PPV of any sputum eosinophils for increased subepithelial eosinophilia was only 36.4%.

CONCLUSIONS

There was moderate agreement between both Fe(NO) and sputum eosinophils and BAL eosinophils. There was good NPV, but only poor PPV for these markers for mucosal eosinophilia.