DPP4 and chronic obstructive pulmonary disease: Study systematically investigated the correlation between serum level of DPPIV and types of COPD, including stable COPD, AECOPD, measuring serum concentrations of DPPIV with ELISA, followed by a comprehensive analysis of the relationships between a set of parameters of COPD and different forms of COPD using statistical analysis methods (Holst and Deacon, 2005; Chang et al., 2016).