Defining asthma COPD overlap syndrome (ACOS): A population based study

<b>Aims</b> – Patients with Asthma COPD Overlap Syndrome (ACOS) are an important clinical phenotype because they experience more exacerbations and may require different treatment. An important challenge is the definition of ACOS. Multiple, but inconsistent, definitions have been proposed. The aims of the present study are to assess the impact of various ACOS definitions on prevalence, patient characteristics and clinical outcomes. <b>Methods</b> – The Netherlands Epidemiology of Obesity study is a population based cohort study in men and women aged 45-65yrs. For the present analysis we included 5,784 individuals and a subpopulation of 864(15%) asthma/COPD patients. ACOS was defined according to six definitions, based on registry, questionnaires and lung function (FEV₁/FVC and FENO). Differences in patient characteristics between definitions were assessed with regression analysis. Exacerbation rates during follow-up were compared. <b>Results</b> – Prevalence of ACOS in the asthma/COPD population ranged between 2.1 and 38.2%, depending on the definition. Agreement between registry-based and self-reported ACOS was 0.04, but increased to 0.40 when lung-function (FEV₁/FVC&lt;0.7) was added. Patient characteristics were similar, but asthma duration was longer with self-reported- compared with registry-based ACOS (mean difference: 22 (95% CI 12-33)yrs). Exacerbation rates were similar between self-reported- and registry-based ACOS (RR 1.24 (95% CI 0.94-1.64)). <b>Conclusion</b> – This study adds important knowledge about the agreement between different ACOS definitions. Given the low agreement between definitions and differences in prevalence, patient characteristics and clinical outcomes, consensus about the definition of ACOS is urgently needed.