[Correspondence] FeNO or no FeNO in COPD?

Stephanie A Christenson and colleagues' post-hoc analysis of the BOREAS trial provides valuable data in The Lancet Respiratory Medicine: they show that blocking the shared interleukin (IL)-4 and IL-13 receptor with dupilumab reduces chronic obstructive pulmonary disease (COPD) exacerbations and that the treatment effect increases with higher baseline blood eosinophil counts and fractional exhaled nitric oxide (FeNO).1