Unravelling the Information Contained in the Single Items of the COPD Assessment Test for Different Outcomes and Smoking Status in Patients with COPD: Results from COSYCONET

The COPD Assessment Test (CAT) comprises eight questions. We evaluated the information that each of the questions and the total score contributed to outcomes and characteristics of chronic obstructive lung disease (COPD), including their dependence on smoking status. Patients with COPD of the COSYCONET cohort with Global Initiative for Chronic Obstructive Lung Disease (GOLD) grades 1-4 and the former grade 0 were included. The evaluated outcomes included mortality, exacerbation risk, the comorbidities asthma, cardiac disease (coronary artery disease/heart failure), osteoporosis, and emphysema, for which a reduction in carbon monoxide transfer coefficient (KCO)