Lung function tests (also called pulmonary function tests) are done to check how well your lungs are working. The test may be done to find the cause of breathing problems, diagnose lung diseases, or find out how well treatment for a lung problem is working.

There are many types of lung function tests.

• Spirometry measures how much and how quickly you can move air out of your lungs. A spirometry test can measure:
  • Forced expiratory volume (FEV), which is the amount of air you can exhale with force in one breath.
  • Peak expiratory flow (PEF), which is how much air you can quickly breathe out when you try your hardest.
  • Total lung capacity (TLC), which is the amount of air in your lungs after you inhale as deeply as possible.
• Gas diffusion tests measure the amount of oxygen and other gases that cross the lungs' air sacs (alveoli) per minute. The results help determine how well gases are being absorbed into your blood from your lungs.
• Inhalation challenge tests help identify substances that may be causing severe respiratory allergies or asthma. These tests are also called provocation studies.