LCN2 and chronic obstructive pulmonary disease: However, in the COPD‐S group, the NE level was strongly correlated with all three analytes, that is MMP‐9 (r = 0.54, P < 0.0001; Fig. 3D), NGAL (r = 0.62, P < 0.0001; Fig. 3E) and proMMP‐9/NGAL (r = 0.52, P < 0.0001; Fig. 3F).