What Are Pulmonary Function Tests?

You will probably be asked to blow — hard, fast, and for longer than feels natural — while a technician coaches you like a trainer at the side of a track. That, in essence, is a pulmonary function test appointment. Pulmonary function tests, often shortened to PFTs, are a group of breathing tests that measure how well your lungs move air in and out and how efficiently they pass oxygen into the blood. They don’t involve cameras or scans of the chest; the information comes from the breath itself.

The video at the top of this page, "Pulmonary Function Tests", runs for about twelve and a half minutes and works through what these tests measure, in the terms the field itself uses: how well the lungs take in and exhale air, how efficiently they transfer oxygen into the blood, and — in the case of spirometry, the best-known test in the group — how well the lungs exhale. Watching it before an appointment is a good way to arrive knowing what the equipment is for.

Arriving at the lab, and what happens first

Expect a fairly ordinary clinic room rather than anything dramatic: a chair, a desktop machine with a screen, disposable mouthpieces, and nose clips. Before any blowing starts, the team will usually record your height, because expected lung volumes are worked out partly from height, and ask about your symptoms, your smoking or vaping history, any inhalers or other medicines you use, and whether you’ve had recent chest or eye surgery, a recent chest infection, or anything else that might affect hard breathing efforts. Be honest about all of it — the answers shape how the results are read.

You may be asked, for some appointments, to avoid using certain inhalers for a set time beforehand, or to skip a heavy meal or vigorous exercise just before. That varies by what your team wants to measure, so follow the instructions on your own appointment letter rather than a general rule, and if you’ve already used an inhaler, just say so — the test can usually still go ahead and be interpreted in that light.

The main event: breathing on instruction

Spirometry is the centrepiece of most appointments. You’ll sit upright, clip your nose closed, seal your lips around a mouthpiece, and follow a very specific pattern: breathe in as deeply as you can, then blast the air out as fast and as completely as you can, and keep going until you’re told to stop. It feels oddly athletic. The machine draws the effort as curves on the screen and calculates, among other things, how much air you can force out in the first second and how much you can empty in total.

One effort is never enough. You’ll normally repeat the manoeuvre several times so the team can see consistent results — this is about technique as much as lungs, and a hesitant start or a cough mid-blow can spoil a reading, so don’t be discouraged if you’re asked to go again. Sometimes spirometry is then repeated after you’ve used an inhaler that opens the airways, to see whether the numbers change; that comparison is a standard part of working out whether narrowed airways can open up again. Our asthma condition hub shows one common setting for exactly that question, and our guide to asthma and how it is treated explains the condition behind many referrals.

Beyond spirometry: the wider panel

Depending on why you were referred, the appointment may add other measurements under the same PFT umbrella. Lung volume tests work out the total size of your lungs and how much air stays behind after you breathe out — one common method has you sitting in a clear booth, a bit like a phone box, breathing against a shutter for a few seconds at a time. A gas transfer test asks how well oxygen moves from the air in your lungs into your blood: you breathe in a harmless test gas mixture, hold your breath briefly, and breathe out while the machine analyses what comes back.

Not everyone gets every test, and the panel is chosen for the question being asked. Breathlessness has many possible causes, and PFTs are one piece of a wider work-up — another video on this site, "Diagnosis and Evaluation of COPD", sets out how a COPD assessment typically combines your history, a physical examination and lung function tests including spirometry. The conditions these tests most often help sort out include COPD and asthma, where airways narrow, and conditions where the lung tissue itself stiffens, such as pulmonary fibrosis. If looking inside the airways is also needed, that is a different procedure entirely — our guide to bronchoscopy covers it.

Afterwards: what the numbers can and cannot say

There’s no recovery time in the usual sense — you can normally drive, eat and get on with your day straight away, though repeated maximal blows can leave you briefly light-headed or tired, and the team will let you sit until that passes. Results are rarely given in full on the spot, because the traces need quality-checking and comparing against expected values for someone of your age, height and sex before a specialist reports them.

What the report can do is describe a pattern: whether the airways look narrowed, whether lung volumes look reduced, whether gas transfer looks impaired, and whether an inhaler changed things. That pattern helps your team confirm or rule out particular causes of breathlessness, grade how severe a known lung condition is, and follow it over time — repeat tests months or years apart are often more informative than any single set. What PFTs cannot do on their own is name a diagnosis in isolation; they are read alongside your symptoms, examination and any imaging. If your numbers are abnormal, that is the start of a conversation with your team, not a verdict to carry home alone.

References & further reading

• MedlinePlus — Pulmonary function tests (Medical Encyclopedia): https://medlineplus.gov/ency/article/003853.htm
• Johns Hopkins Medicine — Pulmonary function tests: https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/pulmonary-function-tests
• American Lung Association — Lung procedures and tests: https://www.lung.org/lung-health-diseases/lung-procedures-and-tests

Frequently Asked Questions

Do pulmonary function tests hurt?

No. There are no needles or instruments inside the body for the standard tests — just breathing through a mouthpiece, sometimes with a nose clip. The forced breathing efforts can feel tiring and may make you cough or feel briefly dizzy, and the team will pause whenever you need.

How long does a PFT appointment take?

Spirometry alone is usually a short appointment, while a fuller panel with lung volumes and gas transfer takes longer. Your appointment letter is the best guide, because the time depends on which tests your team has requested and whether spirometry is repeated after an inhaler.

Can I eat and take my medicines as usual beforehand?

Follow the instructions that come with your appointment, as they differ by test and by what is being measured. Some teams ask you to hold certain inhalers for a time beforehand and to avoid a heavy meal just before; if you have used an inhaler anyway, tell the team rather than cancelling.

What if I can’t manage the hard blows?

Tell the technician — coaching, rest breaks and repeat attempts are a normal part of the process, and young children and people with certain conditions simply do their best. The team records how well the manoeuvres met the quality standard, and that is taken into account when the results are interpreted.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about pulmonary function tests, not medical advice and not a diagnosis. Whether these tests, or any investigation, are right for you is a matter for your own care team, who know your results and your history.