Celli BR, Anderson JA, Brook R, Calverley P, Cowans NJ, Crim C, Dixon I, Kim V, Martinez FJ, Morris A, Newby DE, Yates J, Vestbo J. Serum biomarkers and outcomes in patients with moderate COPD: a substudy of the randomised SUMMIT trial. BMJ Open Respir Res. 2019; 6(1):e000431.