Diffusing Capacity and Mortality in Chronic Obstructive Pulmonary Disease

Rationale: 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_CO) is a potential predictor of mortality that reflects physiology distinct from that in the BODE index. Objectives: This study evaluated DL_CO as a predictor of mortality using participants from the COPDGene study. Methods: 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_CO measurements from the COPDGene phase 2 visit.

wall thickness, and history of cardiovascular or kidney diseases. C statistics for models with DL_CO and BODE scores were used to compare discriminative accuracy. Results: 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_CO percent predicted, mortality increased by 28% (hazard ratio = 1.28; 95% confidence interval, 1.17–1.41, P, 0.001). When compared with other clinical predictors, DL_CO percent predicted performed similarly to BODE (C statistic DL_CO = 0.68; BODE = 0.70), and the addition of DL_CO to BODE improved its discriminative accuracy (C statistic = 0.71). Conclusions: 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_CO in prognostic models for COPD.