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

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

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