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 (FENO) is seen in asthma with Th2-inflammation, justifying FENO as a point-of-care biomarker. The use of FENO in COPD is much less frequent. We aimed to review the evidence in favor of FENO measurement in COPD and discuss its potential usefulness in clinical settings.

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

EXPERT OPINION: There is good evidence that FENO 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 FENO in COPD today. Instead, a personal baseline FENO level should be established when the patient is in a stable phase of the disease, which will subsequently set high and low FENO levels in a personalized manner. In the future, home monitoring of FENO could help identify exacerbations early, allowing proper action to be taken.