Ilumets et al. also mentioned that MMP-8 in the sputum distinguished individuals with asymptomatic COPD, at risk of developing COPD, from healthy smokers, while Sng et al. reported a negative correlation between MMP-8 with exhaled breath condensate in COPD patients when compared to healthy controls [49, 51]. Here, MMP8 is linked to chronic obstructive pulmonary disease.