Pulmonary function tests, or PFTs, typically include a spirometry reading, which tests how much air the patient can breathe in and out and how well the lungs transfer oxygen and carbon dioxide in and out of the bloodstream, according to Healthline. It may also include a plethysmography test, which measures the volume of gas in the lungs.
For the spirometry test, the patient sits in front of a machine, wearing a mouthpiece. The doctor may have the patient breathe deeply or as quickly as possible for several seconds, or the doctor may have the patient breathe in a medication or gas to see how it affects lung function, reports Healthline. For the plethysmography test, the patient goes into a booth where the doctor can assess his lung volume by measuring the amount of pressure within the booth.
A doctor may order a series of PFTs to assess a patient who has symptoms of lung problems, to monitor treatment of a patient who already has a diagnosis of lung disease, to assess lung function prior to surgery or as part of a broader physical exam, explains Healthline. PFTs can diagnose serious conditions such as asthma, chronic bronchitis, lung fibrosis, pulmonary tumors and lung cancer.