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Discussion
This is the first study to focus on both baseline and follow-up characteristics of patients with undiagnosed COPD in China. We found that patients with undiagnosed COPD had a low level of education, a high proportion of biofuel users, current smokers and little COPD-related knowledge. Undiagnosed patients with COPD also at risk of AE and need further caring. Public education is important, especially in high-risk population.
Although COPD is a leading cause of morbidity and mortality worldwide, the disease remains largely undiagnosed and public awareness, particularly knowledge of COPD, is low.20 A Korean study showed that 68% of Indigenous and 19% of non-Indigenous participants reported ‘not knowing/never heard of COPD’.21 In our study, the proportions of ‘know nothing about COPD’ were 49.4%, 68.6% and 34.7% in high-risk populations, undiagnosed and patients with diagnosed COPD, respectively. However, all these populations scored less than 10 points. Interestingly, for the first time, we identified COPD-related knowledge scores as a risk factor for undiagnosed COPD. People who care about their health actively learn more about diseases and thus avoid risk factors or detect abnormal symptoms earlier. Some patients with COPD learn more about the disease after diagnosis, mainly through advice from specialists, treatment and unpleasant symptoms. Educational level could be another explanation, as patients with undiagnosed COPD had the highest proportion of primary school students and below.
The use of biomass is widespread among Chinese people in rural areas, particularly for cooking and heating.22 There is evidence that exposure to the combustion products of biofuel is an important risk factor for COPD,23 but it has not been taken seriously enough internationally.24 Our analysis found that patients with undiagnosed COPD were more likely to use biofuel than high-risk and diagnosed individuals, reminding us that insufficient attention has been paid to the population exposed to biofuels.
Previous studies were largely conducted in developed countries and found no difference in smoking status between diagnosed and patients with undiagnosed COPD.13 25 However, in the current study, we found that the proportion of current smokers is lower and the proportion of former smokers is higher in diagnosed than patients with undiagnosed COPD. Patients with COPD were willing to quit smoking if they knew their diagnosis. Early smoking cessation is essential for this high-risk population and not only for patients with COPD.
Similar to previous studies,7 14 we found that patients with undiagnosed COPD had fewer symptoms than diagnosed patients, but more symptoms than the high-risk population. A similar assessment of symptom severity was performed using CAT and mMRC scores. Some undiagnosed patients with COPD consider the slight worsening of symptoms to be a normal phenomenon with age or reduced activity intensity to match their current symptoms.26 However, adults with undiagnosed COPD are at a higher risk of AEs, pneumonia or death than healthy individuals, even if they are asymptomatic.12
Previous studies had different results of lung function between undiagnosed and diagnosed patients with COPD. Some showed lower ppFEV1 in undiagnosed obstructive lung disease (OLD) than those with a diagnosis,13 same as our findings. Other studies showed higher mean FEV1 among individuals with undiagnosed OLD compared with patients with diagnosed OLD,27 28 while others found no difference of baseline and follow-up lung function existed between undiagnosed and diagnosed patients with COPD.11
In the current study, we identified three additional factors to identify patients with undiagnosed COPD in the high-risk population, including COPD-relevant knowledge and CAT and mMRC scores. Selecting simple information in high-risk populations before pulmonary function testing and bronchodilator testing may help target the suspected COPD population more specifically, especially in the current situation of a lack of medical utilisation and poor accessibility to lung function tests.
We also collected information during follow-up. We found higher lung function value and CAT score at 1-year follow-up than baseline in both patients with undiagnosed and diagnosed COPD. Comprehensive management including pharmacology and non-pharmacology may make sense, although lower rate of treatment and worse treatment adherence were shown in patients with undiagnosed COPD than diagnosed COPD. AEs accrued not only in patients with diagnosed COPD patients but also in patients with undiagnosed COPD. There is a lot of room for intervention in treatments.
There is evidence that health service rates of respiratory diseases are comparable between patients with undiagnosed and diagnosed COPD.29 Undiagnosed disease means missed opportunities for prevention, modification of risk factors and close monitoring of lung function.7 9 Therefore, early detection of COPD is essential. Importantly, previous studies have observed a significant increase in the willingness to quit smoking when the awareness of COPD was raised.30 Public education of COPD-related knowledge is urgently needs to be improved, not only among patients with COPD but also among the entire population, especially high-risk populations. Furthermore, comprehensive management including pharmacology and non-pharmacology treatments is also important and much remains to be done.
To the best of our knowledge, this is the first study to examine the characteristics and risk factors of undiagnosed COPD using a large dataset from a nationwide Chinese survey. However, this study has some limitations. First, much of the information was obtained from the patients’ self-reports, and recall bias was inevitable. Second, using FEV1/FVC <0.7 resulted in overdiagnosis of COPD in the elderly, while using the lower limit of normal (LLN) for the FEV1/FVC ratio resulted in overdiagnosis in younger people.5 Both definitions of COPD had limitations, and the use of fixed FEV1/FVC ratios is not inferior to LLN. Third, the effects of education were complex. Some people take care of their health and learn more about the disease to maintain their health. Other people can learn about the disease by suffering from the illness. A more in-depth analysis of these two groups with longer follow-up periods is required. Forth, the follow-up time of current study is short with 1 year. Studies with longer follow-up are needed, and the pattern of disease evolution needs to be deeply explored.
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