Reversibility testing (Bronchodilator reversibility (BDR) testing with spirometry)
A breathing test that measures your lung function before and after a reliever inhaler, to see whether narrowed airways open up — which helps diagnose asthma.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- Reversibility testing is spirometry done before and after a reliever inhaler, to see whether narrowed airways open up.
- A meaningful improvement supports asthma, but a normal result does not rule it out — asthma varies, and there may be little to reverse on a good day.
- It takes around half an hour because of the wait after the inhaler, and good technique matters, so several breaths are usually recorded.
- It is one of several asthma tests and is read alongside your symptoms, FeNO, peak flow and sometimes blood tests.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Gives an objective measure of whether narrowed airways open up with a reliever.
Anyone who cannot perform reliable, forceful spirometry, including some young children, may not get a usable result.
You do several blows, take the reliever, wait about 15–20 minutes, then blow again. Mild shakiness from the reliever is normal.
Your before-and-after numbers and the size of the change, explained clearly.
You do several blows, take the reliever, wait about 15–20 minutes, then blow again. Mild shakiness from the...
No restrictions — any tremor or faster heartbeat from the reliever settles quickly and you can carry on as normal.
The before-and-after numbers are often discussed with you at the appointment.
If the result is unclear, your clinician may arrange other tests or a treatment trial, or repeat spirometry later.
What is reversibility testing?
Reversibility testing is a breathing test that measures how well your lungs work before and after you take a reliever inhaler. The breathing test itself is called spirometry, which records how much air you can blow out and how fast.
You do spirometry first, then take a dose of a reliever medicine (usually salbutamol), wait about 15–20 minutes, and do spirometry again. If your airways were narrowed and the reliever opens them up, your numbers improve. A clear improvement supports a diagnosis of asthma, where airway narrowing is typically reversible.
The test cannot prove or rule out asthma by itself. If your airways are not narrowed on the day, there may be little to reverse, so a normal result does not exclude asthma. Your clinician reads the result alongside your symptoms 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.
Options at a glance
These are the main approaches described in this guide. The right option depends on the diagnosis, your goals and what your clinician thinks is safe.
Standard bronchodilator reversibility
Spirometry before and after a reliever inhaler (commonly salbutamol), comparing the change in your FEV1 (the air blown out in the first second).
Reversibility in asthma diagnosis
Used to look for the reversible airway narrowing typical of asthma, usually after FeNO or blood tests have not settled the question.
Reversibility in COPD assessment
Sometimes done when chronic obstructive pulmonary disease (COPD) is being considered, to help tell it apart from asthma, though interpretation differs.
Steroid or treatment trial follow-up
Spirometry may be repeated after a period of inhaled steroid treatment to look for improvement over a longer timescale.
Preparing for your test
- Ask which inhalers or medicines to pause beforehand and for how long — reliever and preventer inhalers are often withheld for a set time so they do not mask the result.
- Do not smoke or vape on the day of the test.
- Avoid strenuous exercise, caffeine, alcohol and a heavy meal shortly before the test.
- Wear loose clothing that does not restrict deep breathing.
- Bring a list of all your inhalers and medicines, and your inhalers themselves.
- Tell the team about any heart problems, recent chest or abdominal surgery, or recent eye surgery, as forceful blowing may not be advised.
- Allow extra time, as there is a wait of about 15–20 minutes after the reliever before the second set of blows.
What happens
A respiratory physiologist or nurse first explains and demonstrates the breathing technique. For spirometry you take the deepest breath you can and blow out as hard and as long as you can into a mouthpiece, usually wearing a soft nose clip. You repeat this several times until the readings are consistent.
You are then given a reliever inhaler, usually salbutamol, often through a spacer. After waiting about 15–20 minutes for it to work, you repeat the spirometry. The team compares your before and after numbers, particularly your FEV1, to see how much your airways have opened. The whole visit usually takes around half an hour to 45 minutes, mostly because of the wait.
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.
May not be suitable if…
- Anyone who cannot perform reliable, forceful spirometry, including some young children, may not get a usable result.
- It is the wrong test if the main question is airway inflammation rather than narrowing — FeNO is needed for that.
- Forceful breathing may be unsuitable soon after chest, abdominal or eye surgery, or with certain heart conditions or aneurysms.
- It should not delay urgent treatment of acute breathlessness, and a normal result should not be used to dismiss a convincing history.
Delay or rearrange if…
- You have a current chest infection or cold that may affect the result.
- You have recently had chest, abdominal or eye surgery, or have unstable heart symptoms.
- You have not been told which inhalers to pause, so the result could be masked.
- You are acutely breathless and need treatment rather than testing.
Alternatives to discuss
- FeNO testing to look at airway inflammation.
- Peak flow monitoring at home to look for variability over time.
- Blood eosinophil count as another supporting marker.
- A bronchial challenge test in specialist settings when other tests are inconclusive.
- A trial of inhaled treatment with review of symptoms and lung function.
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.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Gives an objective measure of whether narrowed airways open up with a reliever.
- Supports a diagnosis of asthma when the improvement is clear.
- Helps tell asthma apart from other causes of breathlessness, such as COPD.
- Non-invasive, with no needles or radiation.
- Results are often available at the same appointment.
- Can be repeated to judge response to treatment over time.
Risks & complications
- Light-headedness, dizziness or coughing from the forceful breathing.
- Mild, brief shakiness or a faster heartbeat from the reliever inhaler (salbutamol).
- Needing several attempts to get a good-quality blow, which some people find tiring.
- A normal result in someone who does have asthma, because there was little narrowing to reverse on the day.
- Difficulty performing the test well because of cough, breathlessness or technique.
- Temporary worsening of symptoms triggered by repeated forced breathing.
- Fainting from repeated hard blows.
- Reliever side effects such as a noticeably fast or irregular heartbeat, more likely with heart conditions.
- Strain on a recent surgical or eye wound from the forceful effort, which is why recent surgery is asked about beforehand.
Reversibility testing is low-risk, but it is effort-dependent and the reliever can cause brief shakiness or a faster heartbeat. The main interpretive trap is that a normal result does not rule out asthma, because there may be nothing to reverse on a symptom-free day. Tell the team about heart problems and any recent chest, abdominal or eye surgery before forceful breathing.
Published figures to discuss
Reversibility testing is a low-risk, non-invasive test, so the focus is accuracy rather than complication rates. The reliever (salbutamol) can cause short-lived tremor or a faster heartbeat. Results depend on good technique and on whether there is airway narrowing to reverse on the day, so a normal test does not exclude asthma. Published, defensible numerical complication rates specific to bronchodilator reversibility are limited, so qualitative wording is used rather than invented figures.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Bronchodilator side effects | Commonly mild and short-lived | Tremor, palpitations or feeling shaky can occur after salbutamol. | Guide sourcesClinical context |
| Positive bronchodilator reversibility | Usually defined by a significant FEV1 improvement; thresholds depend on the guideline and context | A positive test supports asthma or asthma-COPD overlap but is not the whole diagnosis. | Guide sourcesClinical context |
| False-negative result | Recognised | Asthma can be normal between attacks, and recent inhaler use or preventer treatment can reduce reversibility. | Guide sourcesClinical context |
| Poor-quality spirometry | Recognised | The before-and-after comparison is only meaningful if both blows meet quality standards. | Guide sourcesClinical context |
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 no physical recovery. Any shakiness from the reliever passes quickly, and you can return to normal activities, work and driving straight away. The main thing afterwards is understanding your before-and-after result.
- Brief light-headedness or coughing after the hard blows.
- Mild, short-lived shakiness or a faster heartbeat from the reliever.
- Feeling you needed practice to get the breathing technique right.
- No change in symptoms — the test measures your airways, it does not treat them.
Aftercare
- Ask for your before and after numbers and the percentage and millilitre change in your FEV1.
- Ask how the result fits with your symptoms and other tests.
- Restart any inhalers you were asked to pause, as advised.
- Keep a note of the result so it can be compared if the test is repeated.
- Ask what happens next if the result is positive, normal or borderline.
- Mention if you felt unwell, very shaky or had palpitations during the test.
- A list of all inhalers and medicines, and the inhalers themselves
- Confirmation of which inhalers to pause and for how long beforehand
- Loose, comfortable clothing
- A note of heart problems or recent chest, abdominal or eye surgery
- A note of your main symptoms and triggers
- Any previous spirometry, FeNO or peak flow results
- Questions about what the change in your numbers means
⚠ Get urgent help if…
- Worsening breathlessness, wheeze or chest tightness during or after the test not relieved by your reliever — seek help.
- Chest pain, palpitations or feeling faint during the test — tell the team immediately.
- Needing your reliever far more often than usual afterwards, or it not lasting.
- Being too breathless to speak in full sentences, eat or sleep — this is an emergency, call 999.
- Lips or fingertips turning blue, or feeling drowsy or confused — call 999.
- A normal result being treated as proof you do not have asthma despite ongoing symptoms — ask for further assessment.
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
Reversibility is judged by the change in your FEV1 (the air you blow out in the first second) after the reliever. UK guidance supports a diagnosis of asthma in adults if FEV1 rises by 12% or more and by 200 ml or more from the starting value; in children aged 5–16, an increase of 12% or more is used. Your clinician interprets this alongside your symptoms and other tests.
A clear improvement points towards reversible airway narrowing, typical of asthma. A smaller change, or a normal starting spirometry with little to reverse, does not rule asthma out. The test cannot measure airway inflammation, cannot grade severity day to day, and is only one part of the diagnosis.
The result reflects your airways on the day of testing. Because asthma varies, a single test is a snapshot, and your clinician may repeat spirometry — for example after a trial of treatment — to build a clearer picture. How often it is repeated depends on your symptoms and response to treatment.
Related tests, treatments or support
Reversibility testing is usually combined with FeNO, peak flow monitoring and sometimes blood eosinophil counts when diagnosing asthma. In UK guidance it often follows FeNO or blood tests when these have not settled the question, and a bronchial challenge test may be considered if results remain inconclusive.
Follow-up & long-term care
Your result is usually discussed at the same visit or a follow-up. Depending on the numbers and your symptoms, the next step may be a treatment trial, further breathing tests, or repeat spirometry later to look for change over time.
- Spirometry may be repeated to track response to inhaled treatment.
- Bring previous results to reviews so changes can be compared.
- Continue inhalers as prescribed once any test-day pause is over.
Repeat, follow-on and what comes next
- Spirometry may need repeating if the blows are not of good enough quality.
- A normal or borderline result often leads to other tests or a treatment trial rather than a firm answer.
- Spirometry is commonly repeated over time to look for change with treatment.
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
- Your before-and-after numbers and the size of the change, explained clearly.
- Interpretation alongside your symptoms and other tests, not in isolation.
- Clear advice on restarting paused inhalers and on next steps.
- A named route to ask questions and arrange any repeat testing or follow-up.
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:
- Whether reversibility is done alone or as part of a fuller breathing-test session (with FeNO or peak flow).
- Who performs and interprets the test — for example a respiratory physiologist, nurse or consultant.
- Whether a consultation and explanation of results are included.
- Whether further tests or a follow-up appointment are needed.
- The clinic or hospital setting and location.
- Whether the spirometry, reliever inhaler, appointment and interpretation are all included.
- Whether any other breathing tests are bundled in or charged separately.
- Who will perform the test and who will explain the result.
- What happens, and what it costs, if the test needs repeating.
- Whether a follow-up appointment or onward referral is included.
- The cancellation and rescheduling policy.
On the NHS? Spirometry with reversibility is widely available on the NHS when clinically indicated; private testing may be used for speed, convenience or as part of a fuller respiratory assessment.
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.
Consent traps
- Treating a normal result as proof there is no asthma.
- Not advising which inhalers to pause, so the result is masked.
- No explanation of the before-and-after numbers in plain language.
- Forceful testing without first asking about heart conditions or recent surgery.
Marketing red flags
- Claims that a single breathing test can definitively diagnose or exclude asthma.
- Promising an instant, guaranteed diagnosis from one visit.
- Selling spirometry as a complete 'lung health check' that catches every problem.
- Quoting a normal result as proof of healthy lungs.
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.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- What were my before and after numbers, and how big was the change in my FEV1?
- Does my result support asthma, and how does it fit with my other tests?
- Which inhalers should I have stopped before the test, and have I restarted them correctly?
- What happens next if my result is positive, normal or borderline?
- Should the test be repeated after a trial of treatment?
- 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?
Frequently asked questions
Is reversibility testing available on the NHS?
Why was I told to stop my inhalers before the test?
Does the test hurt?
Can a normal result rule out asthma?
What does a 'positive' reversibility test mean?
Will the reliever inhaler make me feel odd?
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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: NICE NG245 — Asthma: diagnosis, monitoring and management (recommendations) Asthma + Lung UK (professionals) — Objective diagnostic testing for asthma British Thoracic Society — Quality-assured diagnostic spirometry guide
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.
Related guides: FeNO test (exhaled nitric oxide) · Peak flow monitoring · Bronchial challenge (provocation) test · Body plethysmography (lung volume test) · Bronchial and transbronchial biopsy