Full lung function tests (gas transfer)

What are full lung function tests?

Full lung function tests are a group of breathing tests that go beyond basic spirometry to give a more complete picture of how the lungs are working. They usually include how much air the lungs hold, how fast you can move air, and how well gases pass between the lungs and the blood.

A key part is the gas transfer test (also called transfer factor, TLCO or DLCO). You breathe in air containing tiny, harmless amounts of carbon monoxide and a tracer gas such as helium, hold your breath for about 10 seconds, then breathe out. By measuring how much of the carbon monoxide is taken up, the test shows how well oxygen can move from the lungs into the bloodstream.

These tests help assess conditions such as emphysema, scarring of the lungs (pulmonary fibrosis) and problems with the lung's blood vessels, and they can guide treatment or fitness for surgery.

The tests measure how the lungs are functioning on the day. They do not name a specific disease on their own; results are interpreted alongside your symptoms, examination, imaging and other tests.

Types, options & approaches

There may be different ways to do this. The right approach depends on the clinical question and your circumstances.

Spirometry vs full lung function tests

Full lung function tests build on spirometry. They are chosen when airflow alone does not answer the question, for example to assess lung scarring or emphysema.

Preparing for your test

• Follow any instructions about pausing inhalers beforehand if asked.
• Avoid smoking or vaping for at least 24 hours before, as it affects the gas transfer result.
• Avoid a heavy meal, vigorous exercise and alcohol shortly before the tests.
• Wear loose clothing that allows deep breathing.
• Tell the team if you are anaemic or have had a recent blood transfusion, as this affects gas transfer results.
• Mention recent illness, chest infection, surgery, a heart attack, stroke or eye surgery, which may mean delaying.
• Bring your inhalers and a list of medicines.

What happens

A trained physiologist explains each test and checks it is safe for you. You sit down with a soft clip on your nose so all your breathing goes through your mouth, and you breathe through a mouthpiece.

For the gas transfer test, you breathe out fully, then take a quick, deep breath of air containing tiny amounts of carbon monoxide and a tracer gas, hold your breath for about 10 seconds, and breathe out steadily. For lung volumes and spirometry you do further breathing manoeuvres, some forceful and some gentle. Each is usually repeated to get reliable results, with coaching throughout.

The whole set typically takes around 30–60 minutes. The measurements are recorded and interpreted afterwards by a specialist, alongside your symptoms, history and any imaging.

Is this test right for me?

A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.

Before you decide

Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.

These tests are generally low risk. The tiny amount of carbon monoxide used in the gas transfer test is harmless. The main practical issues are that results depend on good effort and technique, and that gas transfer can be affected by things other than the lungs — such as anaemia or recent smoking — so it is interpreted carefully. As with spirometry, forceful breathing means the tests are usually delayed after certain recent surgery or cardiovascular events.

Published figures to discuss

These tests are safe and non-invasive, and serious complications are rare. The carbon monoxide used in the gas transfer test is at a tiny, harmless level. Because adverse events are so uncommon, robust complication percentages are not well established, so we describe risks qualitatively. The more relevant 'uncertainty' is that results — especially gas transfer — can be affected by effort, technique, anaemia or recent smoking, and must be interpreted carefully.

These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.

What happens afterwards

There is usually no physical recovery — most people feel normal within minutes. 'Afterwards' mainly means waiting for the results to be interpreted.

• Brief breathlessness or light-headedness that quickly passes
• A little coughing after the manoeuvres
• Feeling tired from the effort for a short while
• Waiting a few days to weeks for the results to be explained

Aftercare

• Resume your normal inhalers and medicines as advised once the tests are done.
• Have a drink and rest for a few minutes if you feel light-headed.
• Ask when and how you will get your results.
• Note any symptoms to discuss when the results are explained.
• Attend any follow-up appointment, imaging or further tests arranged.
• Contact the clinic if you feel persistently unwell afterwards, which is unusual.

• Appointment instructions checked (smoking, inhalers, timing)
• Avoided smoking or vaping for 24 hours beforehand
• Note of anaemia or recent blood transfusion
• Note of recent illness, surgery or heart problems
• Inhalers and medicines list brought along
• Questions about what the results will show
• Clear plan for how results will be shared

⚠ Get urgent help if…

• Chest pain during or after the tests — tell the physiologist immediately or seek urgent help
• Severe or persistent breathlessness that does not settle
• Fainting or feeling you might pass out
• Coughing up blood
• Sudden one-sided chest pain with breathlessness afterwards (very rare)
• Any symptom that feels serious — a breathing test should not leave you unwell

Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.

General guidance — it doesn't replace the specific advice your specialist gives you.

Results & realistic expectations

A 'good' result is a set of reliable measurements that, together with your symptoms, examination and any imaging, help your specialist understand how your lungs are working. The pattern across airflow, lung volumes and gas transfer can point towards problems such as emphysema, lung scarring or blood-vessel disease, or be reassuringly normal.

These tests do not name a specific disease on their own, and a normal result does not rule out every lung condition. Gas transfer in particular can be affected by factors outside the lungs, such as anaemia, so results are interpreted with care and sometimes adjusted. They are one important part of the picture, not the whole answer.

The results reflect your lungs on the day of testing. Lung function changes over time and with treatment, so the tests are often repeated to monitor a condition or the effect of a medicine. How often depends on your diagnosis and stability, which your clinician will advise.

Related tests, treatments or support

Full lung function tests are often combined with each other in a single visit, and with a chest X-ray or CT scan, blood tests, or oxygen-level checks, depending on your symptoms. They are usually arranged and interpreted as part of respiratory specialist care.

Follow-up & long-term care

Results are interpreted by a specialist and usually discussed at a clinic appointment or by letter. Depending on the findings, you may have further tests, start or change treatment, or be reviewed at intervals. Any abnormal result should have a clear plan for what happens next.

• Repeat the tests as advised to monitor a known condition
• Avoid smoking and follow treatment between tests
• Tell the team about new symptoms before a monitoring test
• Keep previous results so changes over time can be compared

Repeat, follow-on and what comes next

• Manoeuvres are repeated in one sitting to get reliable, quality-checked results.
• The tests may need redoing if effort or technique made results inconsistent.
• Gas transfer results may be re-checked or adjusted for factors such as anaemia.
• Monitoring tests are repeated over time to track a condition.

Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.

What good aftercare looks like

• Reliable, quality-checked results interpreted by a trained professional.
• Interpretation that accounts for factors such as anaemia and recent smoking.
• A clear explanation of what the results mean alongside your symptoms.
• A plan for any further tests, treatment or monitoring, shared with your GP.
• A contact route if you feel unwell afterwards, which is unusual.

What affects the cost

Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:

• How many tests are included in the set (spirometry, lung volumes, gas transfer)
• Where they are done and the equipment used
• Who interprets and reports the results
• Whether they are combined with imaging or blood tests
• Any follow-up consultation to discuss the results
• Whether repeat tests are needed for monitoring

• Exactly which tests are included in the package
• The fee for the tests and for interpretation and reporting
• Whether a consultation to discuss results is included
• Cost of any additional tests or imaging if recommended
• What happens, and what it costs, if tests must be repeated
• How and when you receive your results
• Whether results are shared with your GP or referring clinician

On the NHS? Full lung function tests are available on the NHS when clinically indicated, usually in a hospital lung function laboratory; private testing is used mainly for speed or convenience.

You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.

Consent traps and marketing red flags

These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.

Choosing a specialist safely

• Check the specialist is on the GMC Specialist Register for this area.
• Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
• You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
• Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
• You're entitled to your total cost in writing — including any follow-up — before you decide.

How Vuemedics verifies every consultant →

Take this to your consultation. A good specialist will welcome every one of these.

• What are these tests looking for in my case?
• Do I need to avoid smoking or pause any inhalers beforehand?
• What will the results change about my diagnosis or treatment?
• What happens if a result is normal, abnormal or inconclusive?
• Could anaemia or other factors be affecting my gas transfer result?
• When and how will I get my results, and who explains them?
• Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
• Will you be the specialist who carries out my test, and who looks after me afterwards?
• What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
• What does a realistic result look like — and what can this test not achieve?
• What are my options, including waiting, doing nothing for now, or choosing a different approach?
• Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
• What is the total cost in writing, including any follow-ups, and how much time do I have to decide?

Find a verified specialist for full lung function tests (gas transfer)

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How we made this page

Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →

Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.

Sources & standards: Asthma + Lung UK — Gas transfer test Royal Free London — Lung function tests: a guide ARTP — lung function testing resources Pulmonary Function Tests — StatPearls (NCBI) British Thoracic Society — quality improvement and standards

Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.

Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.