MMP9 and chronic obstructive pulmonary disease: We found that the mean serum MMP-9 levels in the COPD group were significantly higher in comparison with the control group (149.0 ng/ml versus 26.5 ng/ml; p < 0.0001), as well as those of the controls subgroups with smoking status (27.5 ng/ml in smokers and 25.9 ng/ml in never smokers, p = 0.37 for comparison between both control subgroups).