MPO and Airway obstruction: Several studies have reported an elevation in plasma MPO levels among patients with various respiratory conditions, such as influenza, SARS-CoV-2 infection, exacerbations of chronic bronchitis with airway obstruction, frequent exacerbations of chronic bronchitis with airway obstruction, acute respiratory distress syndrome (ARDS), and sepsis when compared to individuals without these conditions [9–15].