As it is difficult to calculate COPD prevalence using PFT, various studies have estimated COPD prevalence. We showed a higher level than the existing predicted prevalence.[4, 7, 8] The study conducted by John[25] estimated COPD prevalence in 12 countries using a mathematical model, and the prevalence in Korea was 6.2% at that time. As the year was different, it was difficult to directly compare it with the present study. The actual prevalence rate in 2010, which is the nearest year, was 13.1% that was about twice as high than expected, i.e., the number of actual COPD patients is likely to be higher than currently predicted. In our study, patients diagnosed with COPD ranged between 0.5% and 1.0% in the last 8 years. However, those with COPD as per PFTs ranged from 13.1–14.6%, which was 10–20 times more than the actual number of patients diagnosed, i.e., only 1/20 of all COPD patients were diagnosed with COPD by doctors. Excluding those diagnosed with respiratory diseases like TB, asthma, and lung cancer, eight in 10 patients with COPD were likely to be unaware of COPD and other respiratory-related disease and to remain as the potential high-risk group without management or intervention. COPD is a chronic respiratory disease that needs to be managed. Airflow obstruction increases coronary events and mortality[20, 26] and contributes to deaths due to respiratory diseases like pneumonia.[27] Early COPD means early age onset (< 50 years) of COPD, whereas mild COPD represents mild airflow limitation (FEV1 ≥ 80% predicted).[28] Early COPD accounts for 15% of COPD. However, its prognosis was poor with hazard ratio of 6.42 (95%CI 3.39–12.2) for hospitalization and 1.79 (1.28–2.52) for all-cause mortality.[29] Mild COPD causes accelerated FEV1 decline and increased mortality risk than in those without COPD.[28] Although, early and mild COPD patients have substantial disease burden, their treatment strategy was limited because they are likely to be undiagnosed, thus not included in clinical research. Therefore, active COPD finding is recommended in patients with respiratory symptoms and/or risk factors.[30]
To prevent severe conditions and complications and to lower respiratory mortality, COPD should be detected at an early stage, managed,[31] and prioritized groups should be selected. Age, gender, and education are the most important factors related to COPD.[8, 16] In our study, COPD prevalence was higher in older age groups, in men than in women, and at lower education levels. Particularly, those in their 70 s and those aged ≥ 80 years were about 15 times more likely to develop COPD than in their 40 s, men were three times more likely to develop COPD than women, and elementary school graduates were 1.5 times more likely to develop COPD than college graduates. However, patients with COPD were not statistically significant in terms of age; they have a high prevalence and are unlikely to be detected at an early stage and to be managed.
Although COPD prevalence was high in the ever, current, and heavy smokers, only the diagnosis rate of COPD in ever smokers was 2.4 times higher than never smokers, indicating that smoking is the most important cause of COPD.[32] This means that current and heavy smokers with COPD will continue to smoke unless any clinical or health issues is detected. COPD diagnosis provides the motivation to quit smoking.[33] Therefore, only ever smokers have a high diagnosis rate because smokers may have quit smoking after being diagnosed with COPD. However, in our study, most smokers were unaware that they had COPD and continued smoking. PY is the most powerful predictor for COPD.[34] In our study, the higher the PY, the higher the prevalence, and the 4Q group was diagnosed with COPD 2.8 times more than the 1Q group. As the lungs are irreversible once their functions are impaired, medical practitioners should encourage COPD patients who smoke to quit smoking.[35] However, this intervention is not easy because most patients with COPD are not detected.
It has been proven that the older age group, women, low-educated group, and current smokers who have smoked for a long time are more likely to develop COPD. However, we found that these high-risk groups are not diagnosed with COPD in spite of being more likely to develop COPD. Early detection and management of COPD are necessary for personal health and for lowering the social burden of medical expenses.[36] The burden of medical expenses for COPD is a key challenge globally,[3, 37] and the cost of medical treatment for COPD is rapidly increasing in Korea.[38, 39] Therefore, there must be intervention from the public health viewpoint. The study by Kylie[10] argued that screening in primary care needs to be further expanded since COPD is underdiagnosed. Accordingly, countries with health insurance as social insurance should actively consider including PFT in the national benefit services. Moreover, trainings according to clinical guidelines are necessary because primary care practitioners do not have sufficient knowledge and skills to diagnose and treat COPD, [40] and there is a need to strengthen the competencies of the primary medical-oriented COPD management system.[41] Indoor air pollution caused by solid fuel is one of the major threats to COPD in developing countries, where such medical access is difficult. Therefore, it is necessary to actively consider the pedagogical approaches for the awareness of COPD and for providing ventilation rooms periodically.[42]
COPD, a public health threat since 2000s, has been claimed to be intervened and managed.[7] The management of respiratory diseases like COPD will become more important in the future.[43] Nevertheless, there is still no important consensus. The results of our study further consolidated the previous evidence that COPD could be a significant threat to health problems and highlighted the need for further studies.
Strength and limitations
According to the systematic review, there are studies on COPD, but only 0.3% studies used spirometry to measure COPD,[8] and population-based studies might be less than this. Therefore, our study has the advantage of using large-scale clinical data of 25,000 individuals assessed by a reliable diagnostic method, considered as the actual clinical evidence. It is one of the studies to identify that high-risk groups were not diagnosed with COPD. This study also has several limitations. First, as a cross-sectional study, it only shows the association with each variable and does not explain the causal relationship. When smokers are diagnosed with COPD, it is not possible to examine whether they quit smoking. Second, fine dust and indoor air pollution recently increased the incidence of COPD,[44, 45] but factors related to environmental pollution were not controlled in our study. Therefore, studies that consider environmental factors are needed in the future.