Abstract
BACKGROUND: In low- and middle-income countries, such as Vietnam, the population is exposed to multiple risks, leading to frequent allergic asthma, COPD and their overlap (ACO). We aimed to differentiate asthma and COPD, so that recommended treatments can be applied. METHODS: We hypothesized that during life, the cumulative exposure to noxious particles increases the relative prevalence of COPD, while due to immuno-senescence, the prevalence of allergic asthma decreases with age. Among 568 patients with chronic respiratory symptoms, five phenotypes were defined, based on responsiveness to a bronchodilator (BD), diffusion capacity and cumulative smoking. Then the relative prevalence of each phenotype was related with age. RESULTS: the smoker BD irreversible patients were considered "COPD", while the full BD responders and non-smoking BD incomplete responders were "asthmatics". The other patients were ACO, distributed as "like-COPD" or "like-asthma", based on decreased or normal diffusion capacity. The relative prevalence of asthma, COPD and ACO were 26, 42 and 32% (18% "like-asthma", 14% "like-COPD"). CONCLUSION: Vietnamese patients with chronic respiratory symptoms were considered as falling into asthma or COPD groups, based on cumulative smoking, spirometry with reversibility and diffusion capacity. The relative prevalence of asthma and COPD were 44 and 56%, respectively, most of which did not require corticosteroids.