You are very correct that pulmonary function testing is used to identify abnormalities in the lungs or (as the name implies!) with lung function. The test itself is very simple and not distressing. A technologist will ask you to breathe into a mouthpiece (both normal breathing and a so-called 'forced expiration' where you will breathe out as hard as you can), and a machine will measure and record how air moves into and out of your lungs. Pulmonary function tests (or PFTs) can give a physician a lot of information about not only the exchange of gases in the lungs (what they are supposed to be doing) but also the way in which your muscles function to help you take a deep breath.
There are many different disease processes that can result in abnormal PFTs, and if your doctor
thinks that you need PFTs, he or she is probably trying to evaluate something about how you breathe. However, PFTs are NOT the primary way of evaluating for lung cancer and you shouldn't worry
that this is why your physician has ordered the tests. Most commonly, PFTs are used to evaluate people with asthma
or emphysema. In addition, your doctor will go over all of the results with you so that you can ask all of your questions. Please discuss further with your doctor for more information.