Pulmonary Function Testing (PFT): A Simple Guide
Pulmonary function testing, often shortened to PFT, is a group of breathing tests that measure how well your lungs are working. If you have a cough that will not settle, breathlessness, or a known lung condition to monitor, your doctor may recommend it. The tests are non-invasive and simply involve breathing into a mouthpiece in different ways. Here is what to expect.
What PFTs measure
Pulmonary function tests assess several things about your breathing — chiefly how much air your lungs can hold, how much you can breathe out and how quickly, and how efficiently oxygen passes from your lungs into your blood. Together these measures help build a picture of how your lungs are functioning.
- How much air you can forcefully breathe out, and how fast (spirometry).
- The total volume your lungs can hold.
- How well gas transfers from the lungs into the bloodstream.
Why a doctor might recommend PFT
- To investigate persistent breathlessness, wheezing or a long-standing cough.
- To help assess and monitor conditions such as asthma or COPD.
- To check lung function before certain procedures or treatments.
- To track how a known lung condition is changing over time.
What spirometry — the main test — involves
The most common pulmonary function test is spirometry. You take a deep breath in and then blow out as hard and as fast as you can into a mouthpiece, with a soft clip on your nose so all the air goes through the device. You will usually repeat it a few times to get a reliable result, and the technician will coach you through each effort. It takes effort but is not painful, and you can rest between attempts.
How to prepare
- Ask your doctor whether to pause any inhalers before the test, as instructions vary.
- Avoid a heavy meal just beforehand, and avoid smoking on the day.
- Wear loose clothing that does not restrict your chest or tummy.
- Avoid vigorous exercise immediately before the appointment.
Your doctor or the testing team will give you specific instructions, especially about medications, so follow those closely.
Is it uncomfortable?
The tests are safe and non-invasive. Blowing out forcefully can leave you a little light-headed or make you cough briefly, which is normal and passes quickly. If you feel dizzy, the technician will let you rest. There are no lasting after-effects, and you can return to normal activity straight away.
Getting your results
Your results are compared with expected values for your age, height, sex and other factors, and your doctor interprets them alongside your symptoms and history. The findings help guide diagnosis and treatment, and provide a baseline to compare against in future, which is useful for tracking a condition over time.
Where the test is done and what to expect on the day
A pulmonary function test is carried out by a trained technician using a spirometer and, for fuller assessments, additional equipment. The appointment is calm and methodical: you will be asked some questions, your height and weight may be recorded (since these affect the expected values), and the technician will explain and demonstrate each breathing manoeuvre before you try it.
You will usually be seated, with a soft clip placed on your nose so that all your breathing goes through the mouthpiece. The technician coaches you through each effort and lets you rest in between. The whole appointment typically takes a little longer than the breathing itself, to allow for instructions, repeats and rest, but there is no rush and nothing uncomfortable beyond the effort of breathing hard.
How PFT works alongside other tests
Pulmonary function testing rarely stands entirely alone. Your doctor interprets it together with your symptoms, examination and, where relevant, other investigations such as imaging or blood-oxygen measurement. For example, breathlessness can have causes in the lungs, the heart, or elsewhere, so a PFT is one important piece of a larger puzzle.
- It helps distinguish between different patterns of lung problem, guiding diagnosis.
- It provides a baseline to compare against in future, useful for tracking a condition.
- It can show how well a treatment is working over time.
- It supports decisions about further care, including, where relevant, whether oxygen assessment is needed.
Seen this way, a PFT is not a verdict in itself but a valuable measurement that helps your doctor understand your breathing and plan the right next steps.
Getting an accurate result
Pulmonary function tests rely on your effort, so a few simple things help make the result as accurate and useful as possible. The technician guides you through each step, but it helps to know what to expect:
- Give each breathing effort your full effort — blowing out as hard, fast and completely as you can.
- Form a good seal around the mouthpiece so no air escapes around the edges.
- Follow the coaching on when to breathe in fully and when to blow out.
- Rest between attempts; a few repeats are normal to get a reliable, consistent reading.
Because the test depends on your participation, a relaxed, well-coached effort gives a truer picture than a rushed or half-hearted one. There is no need to worry about “getting it wrong” — the technician simply repeats the effort until the readings are consistent.
Understanding your results
Your results are compared against expected values calculated for someone of your age, height, sex and ethnicity, because normal lung capacity varies from person to person. Doctors often look at whether the pattern suggests airways that are narrowed (obstruction), lungs that cannot expand fully (restriction), or a combination — but interpreting this properly takes clinical judgement.
Just as important as a single result is the trend over time. Repeating the test at intervals shows whether a condition is stable, improving or progressing, which guides treatment decisions. Your doctor will explain what your results mean for you and how they fit with your symptoms and history, rather than leaving you to interpret numbers alone.
Why a baseline is so valuable
One of the quietly important benefits of a pulmonary function test is that it gives you and your doctor a baseline — a clear measurement of how your lungs are working at a particular point in time. On its own that is useful; over time it becomes even more so, because comparing later tests against it shows the direction of travel.
For someone with a long-term lung condition such as asthma or COPD, repeating the test at intervals reveals whether things are stable, improving with treatment, or gradually changing. That trend often tells a more useful story than any single result, and it helps guide decisions about medication and care. Even for someone without a known condition, a baseline can be valuable if breathing problems develop later.
This is part of why pulmonary function testing is worth doing properly, with good effort and clear coaching: the better the measurement, the more reliable the comparison in future. Combined with your symptoms and your doctor’s judgement, that picture over time is a powerful tool for keeping your lung health on track.
This article is general information, not medical advice. Your doctor will decide whether pulmonary function testing is needed and interpret your results.
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