Liu S, et al. - In this follow-up study, researchers determined the effect of the new LLN (Lower Limit of Normal) reference equation for Chinese on detecting COPD (Chronic Obstructive Pulmonary Disease), relative to the traditional 0.7fixed criteria. LLN-based COPD detection was found to be consistent with the GOLD(Global initiative for chronic obstructive pulmonary disease) 0.7 fixed-ratio in general. Younger subjects, with more symptoms, more exposure to biofuels and worse FEV₁ than the normal group were noted to be underdiagnosed when LLN was used as the reference diagnostic criterion. Compared with normal group, a little difference was noted in overdiagnosed subjects, except for being older. Overall, influences on detecting airflow limitation were better revealed by individual-dependent LLN. Those who were underdiagnosed by GOLD criterion deserve more attention.