Pulmonary function tests (PFTs) are a group of tests that measure how well the lungs are working. They are used to diagnose and monitor lung conditions such as asthma, chronic obstructive pulmonary disease (COPD), and lung fibrosis, and to evaluate the effectiveness of treatments for these conditions. PFTs typically involve breathing into a machine that measures the volume and flow of air being inhaled and exhaled, as well as the transfer of oxygen and carbon dioxide between the lungs and bloodstream. Common PFTs include spirometry, diffusing capacity, and lung volume tests.