Lung function tests, also known as pulmonary function test is used for the diagnosis of lung disorders such as asthma, respiratory infections, chronic obstructive pulmonary disease (COPD), and others. These group of tests also determine the functioning of the lungs, and the ability of a person to breath. They are also a part of tests for routine examination by the healthcare provider. The healthcare provider may recommend lung function tests to diagnose the suspected lung disease, plan the treatment, and decide whether to continue the ongoing treatment or change it and even to stop the treatment, if required. Therefore, lung function test plays a vital role in the diagnosis of various respiratory diseases, and lung disorders.