Prevalence of airflow limitation in subjects undergoing comprehensive health examination in Japan: Survey of Chronic Obstructive pulmonary disease Patients Epidemiology in Japan.

PURPOSE: There are still evidence gaps on the prevalence of airflow limitation in Japan. The purpose of this survey was to estimate the prevalence of airflow limitation among healthy subjects in Japan and to show what proportion of subjects with airflow limitation had been diagnosed with chronic obstructive pulmonary disease (COPD). SUBJECTS AND METHODS: This was an observational, cross-sectional survey targeting multiple regions of Japan. Subjects aged 40 years or above who were undergoing comprehensive health examination were recruited from 14 centers in Japan. Airflow limitation was defined as having forced expiratory volume in 1 second/forced vital capacity less than 70%. RESULTS: In a total of 22,293 subjects, airflow limitation was most prevalent in subjects aged over 60 years (8.7%), but was also observed in subjects aged 50-59 years (3.1%) and 40-49 years (1.7%). Overall prevalence was 4.3%. Among subjects with smoking history (n=10,981), the prevalence of airflow limitation in each age group (12.8% in those aged over 60 years, 4.4% in those aged 50-59 years, and 2.2% in those aged 40-49 years) and overall prevalence (6.1%) were higher than that of total subjects. Of the smokers with airflow limitation, 9.4% had been diagnosed with COPD/emphysema and 27.3% with other respiratory diseases. CONCLUSION: Among smokers undergoing comprehensive health examination, prevalence of airflow limitation reached 12.8% in those aged over 60 years and airflow limitation was observed in subjects aged 40-59 years as well, though their prevalence was lower than that in subjects aged over 60 years. We demonstrated that a significant proportion of smokers with airflow limitation had not been diagnosed with COPD/emphysema, suggesting that some of them can be diagnosed with COPD or other respiratory diseases by a detailed examination after comprehensive health examination. Screening for subjects at risk of COPD by spirometry in comprehensive health examination starting at 40 years of age, followed by a detailed examination, may be an effective approach to increase the diagnosis of COPD.