Explanation

A pulmonary function test (PFT), also called the lung function test, is a group of tests that helps your doctor check how well your lungs are working. They can check how well air is getting in and out, and how well oxygen is being moved from your lungs to your bloodstream.

Why do I need one?

PFTs are done to check how well your lungs work. Your doctor might want to you to do this test if he or she thinks there might be something wrong with your lungs. It might be to test if you have asthma or bronchitis, or to see how your medicine is affecting your lungs.

What happens before I have it?

Firstly, you should make sure you don't eat too much before the test. Also, it's important to tell your doctor if you have any lung or heart diseases, or if you use inhalers before you do this test. If you are taking asthma medication, your doctor might tell you not to take it for 6-24 hours before the test but check with him or her first. You may need to take your medicine with you so ask your doctor.

How is it done?

Your doctor will first do some measurements, such as weighing you and measuring how tall you are.

There are three main tests that make up the overall lung test. Spirometry measures how much air is getting in and out of your lungs, and how quickly. Another test is a lung volume test which measures the amount of air that your lungs can hold easily. Lastly, a test called diffusion capacity (also called the DLCO) can be done to help your doctor check how well your lungs move oxygen from the air into your bloodstream.

The first test is usually spirometry where you will be given a mouthpiece to breathe into that is connected to a spirometer. Your doctor may tell you to breathe normally, or to breathe fast and deep. He or she might also clip your nose so you only breathe through your mouth into the mouthpiece (this test might feel a bit like snorkelling!).

Your doctor might also ask you to sit in a special booth, called a body plethysmograph, which looks like a glass phone-booth or a shower cubicle. This is used to get a better idea of your breathing and also to test your lung volume. The booth is air-tight so it can be more accurate than using a mouthpiece spirometer. Your doctor may ask to test your lung volume and diffusion capacity by getting you to breathe a special gas through a tube for a short period of time.

These tests usually last for between 30 and 60 minutes but if you get short of breath during the test it can take longer.

Will it hurt?

No, a PFT doesn't hurt at all, but you might feel light-headed or short of breath while doing the test if your doctor has asked you to breathe out hard. You are not in any rush though so take your time until you get your breath back.

What happens next?

You can go home after the test. Your doctor will talk to you about the results when they are ready.

What if I have any other questions?

If you have any other questions, you can ask your doctor, or chat to other people about PFTs in the Medikidz forums and virtual world, Mediland.