MPO and asthma: In patients with asthma, sputum MPO and HNL/NGAL levels showed a positive correlation with sputum neutrophil counts (MPO, r = 0.433, p < 0.001; HNL/NGAL, r = 0.584, p < 0.001) and with each other (r = 0.628, p < 0.001).