Diffusing Capacity and Mortality in Chronic Obstructive Pulmonary Disease.

Chronic obstructive pulmonary disease (COPD) mortality risk is often estimated using the BODE (body mass index, obstruction, dyspnea, exercise capacity) index, including body mass index, forced expiratory volume in 1 second, dyspnea score, and 6-minute walk distance. Diffusing capacity of the lung for carbon monoxide (Dl) is a potential predictor of mortality that reflects physiology distinct from that in the BODE index. This study evaluated Dl as a predictor of mortality using participants from the COPDGene study. We performed time-to-event analyses of individuals with COPD (former or current smokers with forced expiratory volume in 1 second/forced vital capacity < 0.7) and Dl measurements from the COPDGene phase 2 visit. Cox proportional hazard methods were used to model survival, adjusting for age, sex, pack-years, smoking status, BODE index, computed tomography (CT) percent emphysema (low attenuation areas below -950 Hounsfield units), CT airway wall thickness, and history of cardiovascular or kidney diseases. C statistics for models with Dl and BODE scores were used to compare discriminative accuracy. Of 2,329 participants, 393 (16.8%) died during the follow-up period (median = 4.9 yr). In adjusted analyses, for every 10% decrease in Dl percent predicted, mortality increased by 28% (hazard ratio = 1.28; 95% confidence interval, 1.17-1.41,  < 0.001). When compared with other clinical predictors, Dl percent predicted performed similarly to BODE (C statistic Dl = 0.68; BODE = 0.70), and the addition of Dl to BODE improved its discriminative accuracy (C statistic = 0.71). Diffusing capacity, a measure of gas transfer, strongly predicted all-cause mortality in individuals with COPD, independent of BODE index and CT evidence of emphysema and airway wall thickness. These findings support inclusion of Dl in prognostic models for COPD.