Comparison of Diagnostic Criteria of ACO: What Is the Point of Difference?

Now, patients with both features of asthma and chronic obstructive pulmonary disease (COPD) are demonstrated to have greater respiratory symptoms, frequent exacerbations, and poor quality of life compared to those with asthma or COPD alone and are widely recognized as asthma-COPD overlap (ACO). Until recently, various diagnostic algorithms of ACO have been proposed around the world, but there is no single universally accepted definition for ACO. In this chapter, we describe the diagnostic criteria of ACO in the recent literature, including Japanese Respiratory Society’s proposal and compare them to clarify how they differ. There are variations in the diagnostic criteria based on only the symptoms or, additionally, employing several objective diagnostic tests including the bronchodilator response in forced expiratory volume in 1 s, blood or sputum eosinophil count, serum IgE levels, and fractioned exhaled nitric oxide. The difference could be partly due to the limited accessibility to diagnostic tests. However, there have not been enough concrete data to support using these diagnostic criteria in ACO. Further large longitudinal data are required to validate these diagnostic criteria of ACO for an accurate diagnosis and proper treatment.