Heterogeneous burden of lung disease in smokers with borderline airflow obstruction

BACKGROUND: The identification of smoking-related lung disease in current and former smokers with normal FEV(1) is complex, leading to debate regarding using a ratio of forced expiratory volume in 1 s to forced vital capacity (FEV(1)/FVC) of less than 0.70 versus the predicted lower limit of normal (LLN) for diagnosis of airflow obstruction. We hypothesized that the discordant group of ever-smokers with FEV(1)/FVC between the LLN and 0.70 is heterogeneous, and aimed to characterize the burden of smoking-related lung disease in this group. METHODS: We compared spirometry, chest CT characteristics, and symptoms between 161 ever-smokers in the discordant group and 940 ever-smokers and 190 never-smokers with normal FEV(1) and FEV(1)/FVC > 0.70 in the SPIROMICS cohort. We also estimated sensitivity and specificity for diagnosing objective radiographic evidence of chronic obstructive pulmonary disease (COPD) using different FEV(1)/FVC criteria thresholds. RESULTS: The discordant group had more CT defined emphysema and non-emphysematous gas trapping, lower post-bronchodilator FEV(1) and FEF(25–75), and higher respiratory medication use compared with the other two groups. Within the discordant group, 44% had radiographic CT evidence of either emphysema or non-emphysematous gas trapping; an FEV(1)/FVC threshold of 0.70 has greater sensitivity but lower specificity compared with LLN for identifying individuals with CT abnormality. CONCLUSIONS: Ever-smokers with normal FEV(1) and FEV(1)/FVC < 0.70 but > LLN are a heterogeneous group that includes significant numbers of individuals with and without radiographic evidence of smoking-related lung disease. These findings emphasize the limitations of diagnosing COPD based on spirometric criteria alone. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12931-018-0911-z) contains supplementary material, which is available to authorized users.