Lung function
Full lung function tests
The complete laboratory assessment of your lungs - volumes, capacities and gas exchange, beyond what spirometry can see.
Key facts
At a glance
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What is included: spirometry plus total lung volumes (measured in a body box) and gas transfer - how well oxygen crosses into the blood.
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On the day: a series of breathing manoeuvres through a mouthpiece, some inside a glass booth; allow 45-90 minutes.
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Preparation: inhaler withholding instructions and no smoking, alcohol, heavy meals or vigorous exercise beforehand.
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Who needs it: unexplained breathlessness, suspected lung scarring or restriction, pre-surgical assessment and monitoring of known disease.
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Follow-up: a respiratory physician interprets the full pattern - obstruction, restriction, hyperinflation or gas transfer defects.
The full picture
What this test involves, and how to get it
Full lung function testing extends spirometry in two crucial directions. Static lung volumes, measured in a body plethysmograph - a glass booth you sit inside while making gentle panting efforts - reveal the total size of your lungs and how much air remains trapped after full exhalation, distinguishing true restriction (small lungs, suggesting scarring or chest wall disease) from the hyperinflation of emphysema. Gas transfer (TLCO) measures how efficiently a test gas crosses from the air sacs into the blood, probing the lung’s working surface: it falls in emphysema, pulmonary fibrosis and pulmonary vascular disease, sometimes before anything shows on X-ray. Together these produce a physiological fingerprint that spirometry alone cannot.
The session lasts up to ninety minutes of coached breathing manoeuvres - undemanding but repetitive - with the usual pre-test rules about inhalers, smoking and heavy exertion. Full testing is the right tool for unexplained breathlessness with normal basic tests, suspected interstitial lung disease, sarcoidosis, pre-operative assessment before lung or major surgery, and monitoring conditions and drug effects (some medications require serial gas transfer checks). NHS lung function laboratories operate in hospitals with waits tied to respiratory clinic demand; private hospitals run the same laboratories with appointments typically inside one to two weeks, and results reviewed with a respiratory physician rather than posted as bare numbers.
A quiet reminder
This guide is for information, not medical advice.
Your own clinician knows your history and can tell you which parts apply to you. Next review of this page: 2027-09-27.
Frequently asked
Common questions about Full lung function tests.
Quick, plain-English answers to what people ask us most.
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What are full lung function tests?
Full lung function tests, also called pulmonary function tests, measure how well your lungs work by assessing lung volume, airflow, and how efficiently oxygen passes into your blood. They typically combine spirometry with additional measurements like lung volumes and gas transfer.
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Why would a doctor order full lung function tests?
They're used to investigate breathlessness, chronic cough, or wheeze, and to diagnose and monitor conditions such as asthma, COPD, and interstitial lung disease. They're also useful before certain surgeries to assess lung capacity beforehand.
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Do I need to prepare for it?
You may be asked to avoid smoking, heavy meals, and certain inhalers for a few hours before the test, as these can affect results. Your clinic will give you specific instructions based on which tests are included.
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What happens during the test?
You'll breathe through a mouthpiece in various ways, such as blowing out hard and fast, breathing normally in a sealed booth, or inhaling a small amount of tracer gas, depending on which measurements are being taken. The full assessment typically takes 30 to 60 minutes.
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Does it hurt or have risks?
The tests are not painful, though some of the breathing manoeuvres can feel tiring or make you briefly light-headed. They're very safe overall, with staff monitoring you throughout.
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How long do results take?
Basic results are often available on the day, with a full specialist report usually following within a few days.
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What do abnormal results mean, and what happens next?
Results can point towards a range of conditions, from asthma and COPD to less common lung diseases, and the pattern of abnormalities helps guide diagnosis. Your doctor will explain what the results show and discuss any further tests, such as imaging, or treatment options.
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How much does it cost privately, and is it available on the NHS?
Full lung function testing is available on the NHS through respiratory clinics, usually via GP or specialist referral, though waits can be lengthy for non-urgent cases. Private testing is typically available within one to two weeks, with specialist review included, and cost varying by provider.
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Is it accurate and reliable?
These tests are well-established and considered the gold standard for assessing lung function, though results depend on good technique and effort during the breathing manoeuvres. Trained staff will guide you to get the most reliable readings.
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How do I book it privately, and how quickly can I be seen?
You can book a private lung function assessment, often alongside a respiratory specialist consultation, with appointments typically available within one to two weeks.