The relationship between the fraction of exhaled nitric oxide and the level of asthma control

The evaluation of asthma control, based on symptoms and risk factors for exacerbation does not provide information about airway inflammation, reflected by fractional exhaled nitric oxide (FeNO). The impact of FeNO in the evaluation of asthma control has not been well recognized. The purpose of this study was to evaluate the contribution of FeNO measurement in the assessment of asthma control.

A prospective cross-sectional study was carried out for four months and included 148 adult asthmatics. For each patient, the demographic data, asthma control test (ACT) score, medication adherence, skin prick test positivity, FeNO level, and spirometry results were recorded independently. The correlation between ACT score and FeNO level was analyzed.

The mean ACT score was 20.9±3.7 and the mean exhaled FeNO level was 30.4±25.8 ppb. Asthma was controlled in 71.6% of patients. Mean FeNO values were significantly higher in patients with uncontrolled asthma (42.1±30.8 versus 27±19 ppb, p=0.01). A significant negative correlation was observed between FeNO level and ACT score (r=-0.33, 95% confidence interval [CI], -0.51-0.10; p=0.001). FeNO had a high negative predictive value (79.9%) and specificity (63.2%), but a low sensitivity (59.5%) and positive predictive value (39%). The area under the receiver operating characteristic (ROC) curve was of 0.7 (95% confidence interval [CI], 0.53-0.74; p=0.01).

Using just FeNO to evaluate asthma control represents a limited approach because of the low predictive accuracy of FeNO for diagnosing uncontrolled asthma.