Predicting an accelerated lung function decline in smokers: is there a proper threshold?

We read, with very much interest, the publication by AKKERMANS et al. [1] in the European Respiratory Journal. In this study they reanalysed data from the first Lung Health Study by forming four groups, based on the forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ,0.70 or ,5th percentile, according to the LMS (lambda, mu, sigma) approach. However, we do have some remarks concerning the validity of their analysis and propose a means of reinterpretation of their outcome. AKKERMANS et al. [1] concluded that the decline of the post bronchodilator FEV1 in the group fixed/LMS (FEV1/FVC ,0.70 and .5th percentile) was significantly lower compared to the group fixed/LMS (FEV1/ FVC ,0.70 and ,5th percentile). The mean¡SD decline was 43.8¡50.0 mL?year versus 53.5¡51.5 mL?year, respectively, and thus one recommended the use of the 5th percentile threshold to define the presence of chronic obstructive pulmonary disease (COPD).