FENO measurement and sputum analysis for diagnosing asthma in clinical practice

Abstract

Objectives: To determine the diagnostic accuracy of fractional exhaled nitric oxide (FENO) measurement in pneumologists routine diagnostic work-up; and to determine the impact of the inflammatory pattern on diagnostic accuracy. Methods: Prospective diagnostic study in 393 patients attending a private practice of pneumologists with complaints suspicious of obstructive airway disease (OAD). Index test was FENO measurement. Reference standard was the Tiffeneau ratio (FEV1/VC) or airway resistance as assessed by whole body plethysmography, with additional bronchoprovocation or bronchodilator testing. Morning sputum was analysed with smear slides which were prepared and stained by Giemsa. Results: 154 patients were diagnosed as having asthma (145 diagnoses based on bronchial provocation, 9 based on bronchodilator results), 5 had COPD. For the whole group, asthma could be ruled in at FENO > 71 ppb (PPV 80%; 95% CI 63-90%) and ruled out at FENO ≤ 9 ppb (NPV 82%; 95% CI 67-91%) (area under the curve (AUC) = 0.656; 95% CI 0.600-0.712; p < 0.001). 128 patients delivered sputum. FENO was 44.3 ppb (sd 48.9) in patients with predominant eosinophilic inflammation, 18.5 ppb with neutrophilic inflammation, and 23.1 ppb in others (p = 0.003). Diagnostic accuracy of FENO increased when patients with neutrophilic inflammation were omitted from analysis (AUC = 0.745; 95% CI 0.651-0.838; p < 0.001). Then asthma could be ruled in at FENO > 31 ppb (PPV 82%; 95% CI 63-92%) and ruled out at FENO ≤ 12 ppb (NPV 81%; 95% CI 62-91%). Conclusions: FENO measurement can be useful as an additional diagnostic tool in pneumologists' practice. The diagnostic value of FENO could be improved when inflammatory patterns are taken into account.© 2012 Elsevier Ltd. All rights reserved.