Measuring exhaled nitric oxide in COPD: from theoretical consideration to practical views.

Introduction: Chronic obstructive pulmonary disease (COPD) is traditionally perceived as Th1-inflammation, but some patients have Th2-inflammation. A high fraction of exhaled nitric oxide (FE) is seen in asthma with Th2-inflammation, justifying FE as a point-of-care biomarker. The use of FE in COPD is much less frequent. We aimed to review the evidence in favor of FE measurement in COPD and discuss its potential usefulness in clinical settings.

Areas Covered: This review covers nitric oxide production in the airways and FE measurements in COPD patients during stable conditions and acute exacerbation. It discusses why COPD patients may have both low and high FE levels and the potential clinical utility of FE.

Expert Opinion: There is good evidence that FE increases with an exacerbation irrespective of the initial low or high baseline value. However, there is insufficient evidence to establish a fixed cutoff value for elevated FE in COPD today. Instead, a personal baseline FE level should be established when the patient is in a stable phase of the disease, which will subsequently set high and low FE levels in a personalized manner. In the future, home monitoring of FE could help identify exacerbations early, allowing proper action to be taken.