Exhaled NO is a poor marker of asthma control in children with a reported use of asthma medication: a pharmacy-based study

BACKGROUND: A high fraction of nitric oxide in exhaled breath (FeNO) has been suggested to be a marker of ongoing airway inflammation and poorly controlled disease in asthma. The usefulness of FeNO to monitor asthma control is still debated today.

AIM: To assess the validity of FeNO as a marker of asthma control in children with reported use of asthma medication.

METHODS: Fraction of nitric oxide in exhaled breath was measured in 601 children (aged 4-12 yr) with reported use of asthma medication in the past 6 months and in 63 healthy non-asthmatic children (aged 5-12). Asthma control was assessed by the Asthma Control Questionnaire (ACQ). A receiver-operator characteristics (ROC) curve was generated to assess the accuracy of FeNO as a marker for asthma control. Logistic regression analysis was used to study whether clinical, healthcare, medication, and environmental factors are associated with high FeNO levels (>25 ppb).

RESULTS: Fraction of nitric oxide in exhaled breath had a poor accuracy to discriminate well-controlled from not well-controlled asthma [area under the ROC curve: 0.56 (95% CI: 0.52-0.61, p = 0.008)]. In addition, high FeNO (>25 ppb) was associated with lower medication adherence rates (OR: 0.4; 95% CI 0.3-0.6), fewer antibiotic courses in the past year (OR: 0.6; 95% CI: 0.4-0.9), fewer leukotriene antagonists use in the past year (OR: 0.4; 95% CI: 0.2-0.9), and fewer visits to a (pulmonary) pediatrician (OR: 0.6; 95% CI: 0.4-0.9). Children living in a non-urban environment had more often high FeNO levels (OR: 1.7; 95% CI: 1.1-2.6).

CONCLUSION: High FeNO is a poor marker of asthma control in children with reported use of asthma medication. Various other factors, including medication adherence and medication use, are associated with increased FeNO levels.