Lung function tests (also known as pulmonary function tests or PFTs) are a group of diagnostic tests used to assess how well your lungs are working. These tests measure the volume of air you can inhale and exhale, how quickly you can exhale, and how well oxygen moves from your lungs into your bloodstream. They are commonly used to diagnose and monitor lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and other conditions affecting the respiratory system.