The association between transfer coefficient of the lung and the risk of exacerbation in asthma-COPD overlap

Abstract

<b>Background:</b> Since low diffusing capacity of the lung for carbon monoxide (D_LCO) is known as a strong risk factor for exacerbation in chronic obstructive pulmonary disease (COPD), D_LCO or a transfer coefficient (K_CO) is speculated to also be associated with the risk of exacerbations in asthma–COPD overlap (ACO). <b>Aims and objectives:</b> To assess the clinical usefulness of D_LCO and K_CO in predicting future exacerbations among ACO patients. <b>Methods:</b> This study was conducted as an observational cohort survey. D_LCO and K_CO were measured in 90 patients with ACO aged ≥ 40 years. Multivariable-adjusted hazard ratios (HRs) for the exacerbation-free rate over one year were estimated and compared across the levels of D_LCO and K_CO. <b>Results:</b> Low K_CO (&lt; 80% per predicted) was positively associated with the incidence of exacerbation (multivariable-adjusted HR = 3.71 (95% confidence interval 1.32–10.39)). The association between low D_LCO (&lt; 80% per predicted) and exacerbations showed similar trends, although it failed to reach statistical significance (multivariable-adjusted HR = 1.31 (95% confidence interval 0.55–3.11)). <b>Conclusions:</b> Low K_CO was a significant risk factor for exacerbations among patients with ACO.