IL6 and chronic obstructive pulmonary disease: Blood IL-6 concentrations (but not other markers of systemic inflammation) correlated with lung function parameters (FEV1 % predicted: r = −0.33, p = 0.015; IVC % predicted: r = −0.42, p = 0.002; MEF50 % predicted: r = −0.27, p = 0.049), the 6 minute walk test (6-MWT) distance (r = −0.51, p = 0.001), the CAT score (r = 0.34, p = 0.012) and the mMRC score (r = 0.41, p = 0.002) in patients with COPD (Additional file 1: Figure S5).