Despite these differences, both methods identified analytes associated with epithelial repair (HB-EGF and TGF-α) and neutrophil function (EN-RAGE, MPO and NGAL) as significant, the latter being consistent with the hypothesis that neutrophil levels are strongly associated with the development of COPD, increasing COPD severity and FEV1 decline. Here, MPO is linked to chronic obstructive pulmonary disease.