Abstract
A weak correlation between diffusing capacity of the lung for carbon monoxide (DL(CO)) and emphysema has been reported. This study investigated whether impaired DL(CO) in chronic obstructive pulmonary disease (COPD) is associated with increased risk of acute exacerbation independent of the presence or extent of emphysema. This retrospective cohort study included patients with COPD between January 2004 and December 2019. The participants were divided into four groups based on visually detected emphysema and impaired DL(CO). Among 597 patients with COPD, 8.5% had no emphysema and impaired DL(CO) whereas 36.3% had emphysema without impaired DL(CO). Among the four groups, patients with impaired DL(CO) and emphysema showed a higher risk of moderate-to-severe or severe exacerbation than those with normal DL(CO). Impaired DL(CO) was an independent risk factor for severe exacerbation (hazard ratio, 1.524 [95% confidence interval 1.121-2.072]), whereas the presence of emphysema was not. The risk of moderate-to-severe or severe exacerbation increases with the severity of impaired DL(CO). After propensity-score matching for the extent of emphysema, impaired DL(CO) was significantly associated with a higher risk of moderate-to-severe (p = 0.041) or severe exacerbation (p = 0.020). In patients with COPD and heterogeneous parenchymal abnormalities, DL(CO) can be considered an independent biomarker of acute exacerbation.