In the GWAS analysis the primary association will be COPD status defined as GOLD Stages 2–4 in smokers with controls being smokers with normal spirometry (post-bronchodilator FEV1/FVC > 0.7 and FEV1 > 80% predicted). Other outcome measures for genetic association will be post-bronchodilator FEV1 – used as a continuous variable in COPD cases, emphysema (% of lung <−950 HU – used as a continuous variable in COPD cases), air trapping on expiratory CT (% of lung < −856 HU – used as a continuous variable in COPD cases) and airway disease as a continuous variable (wall area percent of the 4th and 5th generation airways).
