Pulmonary function test (PFT, spirometry)
Quick answer: A pulmonary function test measures how much air your lungs hold and how fast you can breathe it out, by blowing into a mouthpiece. Doctors order it for long-standing cough or breathlessness, to diagnose or follow asthma or COPD, and sometimes before surgery.
- SampleBreathing test (no sample)
- TakesAbout 15 to 30 minutes, longer if an inhaler is given and the test repeated
- Before the testAvoid smoking and a heavy meal for a few hours before, and ask your doctor whether to take your usual inhalers on the day.
How the test is done
- 1You sit upright and a soft clip is put on your nose
- 2You seal your lips around a mouthpiece connected to the machine
- 3You take the deepest breath you can, then blow out as hard and fast as possible
- 4This is repeated a few times, and may be repeated after an inhaler to see if it helps
What your results can mean
Reading your report
Results are compared with values expected for your age, height and sex; your doctor will explain what they mean for you.
If the result is outside the usual range
Results can show a blocked or narrowed airway pattern, seen with asthma or COPD, or a restricted pattern where the lungs hold less air, which can be seen with lung scarring, chest wall problems or obesity. Improvement after an inhaler can point towards asthma.
Who usually has this test
People with long-standing cough, wheeze or breathlessness, people with asthma or COPD being followed up, and some people before surgery.
Risks and aftercare
You may feel briefly light-headed, tired or short of breath from the hard blowing, which settles with rest.
Names and options
Also called: PFT, spirometry, lung function test, breathing test
Listed by the hospital as
- PFT
Questions about this test
What is FEV1 on a spirometry report?
FEV1 is the amount of air you can blow out in the first second of a hard breath. It is compared with what is expected for your age, height and sex.
Can spirometry diagnose asthma?
Spirometry helps diagnose asthma, especially when the results improve after an inhaler. Doctors use it alongside your symptoms and sometimes other tests.
Should I take my inhaler before a lung function test?
Some inhalers can change the results, but do not stop any medicine on your own. Ask your doctor or the hospital what to do with your inhalers on the day.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.