When comparing sputum MPO and HNL/NGAL levels among the subgroups based on asthma severity (Fig. 2), patients with moderate-to-severe persistent asthma showed significantly higher sputum MPO levels than those of patients with intermittent asthma (407.6 [57.8–1,085.0] vs. 43.5 [13.2–141.4 ng/mL], p < 0.001). This evidence concerns the gene MPO and asthma.