Furthermore, the correlations between the serum levels of MMP‐2, MMP‐3, MMP‐12 on one the hand and MMP‐9, NGAL, the complex and NE on the other were also evaluated in the COPD‐S group: we identified a single, negative correlation between MMP‐2 and NE (r = −0.293, P = 0.04; Table S2). Here, MMP9 is linked to chronic obstructive pulmonary disease.