[Lung function test for COPD].

According to the guideline presented by Global Initiative for Chronic Obstructive Lung Disease(GOLD), the diagnosis of chronic obstructive pulmonary disease (COPD) has been simplified. COPD is diagnosed when FEV1(forced expiratory volume in one second)/FVC(forced vital capacity) is less than 70% (except Stage 0), and also the severity of disease is classified by FEV1. In this article, spirometry, a screening test for COPD, is explained at first, and then further examination to understand the pathophysiology of COPD is discussed. For management and following-up of COPD, both lung function test and arterial blood gas analysis are important.