The predictive value of exhaled nitric oxide measurements in assessing changes in asthma control

Exhaled nitric oxide (eNO) levels are increased in untreated or unstable as thma and measurements can be made easily. Our aim was to assess the usefuln ess of eNO for diagnosing and predicting loss of control (LOC) in asthma fo llowing steroid withdrawal. Comparisons were made against sputum eosinophil s and airway hyperresponsiveness (AHR) to hypertonic saline (4.5%). Seventy -eight patients with mild/moderate asthma had their inhaled steroid therapy withdrawn until LOC occurred or for a maximum of 6 wk. Sixty (77.9%) devel oped LOC. There were highly significant correlations between the changes in eNO and symptoms (p < 0.0001), FEV1 (p < 0.002), sputum eosinophils (p < 0 .0002), and saline PD15 (p < 0.0002), and there were significant difference s between LOC and no LOC groups. Both single measurements and changes of eN O (10 ppb, 15 ppb, or an increase of > 60% over baseline) had positive pred ictive values that ranged from 80 to 90% for predicting and diagnosing LOC. These values were similar to those obtained using sputum eosinophils and s aline PD15 measurements. We conclude that eNO measurements are as useful as induced sputum analysis and AHR in assessing airway inflammation, with the advantage that they are easy to perform.