Knowledge

Lung-function testing (spirometry): how it works.

Lung-function testing is at the core of respiratory assessment. It is painless, takes only a short time and provides objective numbers for how your lungs are working: numbers that, together with your history, form the basis for diagnosis and treatment.

FAQ

Frequently asked questions about lung-function testing.

How is a lung function test done?

You sit down with a soft clip on your nose and blow out as hard and as long as you can into a mouthpiece. The measurement is repeated a few times, and in a reversibility test it is repeated again after airway-opening medication. You get the result before you leave.

What must I avoid taking before a breathing test?

Some inhaled medication must be paused, or the test shows the medicine rather than your lungs. Only pause if the clinic has asked you to. The pause times are listed on this page.

Does it hurt?

No. The test is painless. Some people feel briefly light-headed from the forceful blows, and that passes on its own.

Does a normal result rule out asthma?

No. Lung function is often entirely normal between symptom periods. If the suspicion remains, the next step is a bronchial provocation test.

What does it measure?

Spirometry measures how much air you can blow out and how fast it goes. The two key numbers are FEV1 (the amount of air you can blow out in the first second) and FVC, the total amount of air you can blow out after a full breath in. The relationship between them, and the flow-volume curve the test draws, show whether the air moves freely through your airways or something is slowing it down.

The pattern in the curve and the numbers help distinguish between different causes of breathlessness and cough: for example whether the airways are narrowed, as in asthma, or whether the explanation lies elsewhere. Your results are compared with expected values for your age, height and sex, and at follow-up visits they can be tracked over time, so the effect of treatment can be measured objectively.

How the test is done.

The test requires no needles and does not hurt, but it does require your best effort on each blow. The staff guide you the whole way, and most people get the hang of it after a try or two.

  1. You sit down and get ready

    You are seated throughout the test and get a soft clip on your nose, so all the air passes through your mouth.

  2. You blow into a mouthpiece

    You take a full breath in and then blow out into a mouthpiece as hard and as long as you can. The measurement is typically repeated a few times to make sure the numbers are reliable.

  3. Reversibility testing, if relevant

    The measurement is often repeated after you inhale airway-opening medication. If the numbers improve clearly, it can point towards asthma. This is called a reversibility test.

  4. Your results, straight away

    The results are reviewed with you on the spot: what the numbers show, what they mean for you, and what the next step is.

It is fine if it feels strenuous

A maximal blow can feel strenuous, and some people cough briefly afterwards. That is entirely normal and passes within moments. You can take short breaks between the blows, and the test is always paced to suit you. The whole examination, including any reversibility testing, is typically completed within the same consultation.

Other tests at the clinic

Spirometry rarely stands alone. Depending on your symptoms, it can be supplemented with:

FeNO measurement

Measures inflammation in the airways via your exhaled breath. Quick and simple. You blow steadily into a device.

Bronchial provocation testing

Mannitol, methacholine, EVH or an exercise challenge: used when the diagnosis calls for it, for example with suspected exercise-induced asthma.

Impulse oscillometry (IOS)

Measures the resistance in the airways while you breathe quietly. There is no forced blowing manoeuvre, so it can be used when a standard lung function test is difficult to perform, and as a supplement to it.

Allergy work-up

Skin-prick testing and/or a blood test (specific IgE) when allergy may play a part in your symptoms.

All services and investigations

How to prepare.

You do not need to do much, but a few simple things make the numbers more reliable:

  • Avoid strenuous physical exertion in the last hour before the test.
  • Avoid a large meal in the last couple of hours and smoking/nicotine in the last hour.
  • Arrive in good time, so you are not out of breath when we start.
  • Important information about your medication: only pause your inhaled medication if the clinic has asked you to. If the clinic has given you instructions (for example when you booked or in a message), follow them, and call the clinic if you are in doubt. The clinic's standard pause times are:
    Spirometry (lung function): short-acting reliever (e.g. salbutamol): 6 hours · long-acting beta2 agonist (e.g. formoterol, salmeterol): 24–36 hours · ultra-long-acting beta2 agonist (e.g. vilanterol, indacaterol): 48 hours · ipratropium (e.g. Atrovent): 12 hours · long-acting anticholinergic (e.g. tiotropium): 36–48 hours · preventer (inhaled corticosteroid): continue as usual.
    Provocation test: short-acting reliever (e.g. salbutamol): 8 hours · long-acting beta2 agonist (e.g. formoterol, salmeterol): 36–48 hours · ultra-long-acting beta2 agonist (e.g. vilanterol, indacaterol): 48 hours · ipratropium (e.g. Atrovent): 12 hours · long-acting anticholinergic (e.g. tiotropium): 7 days · inhaled corticosteroid and montelukast: as agreed · antihistamine (allergy medication): 3 days.
    EVH test: short-acting reliever (e.g. salbutamol): 8 hours · long-acting beta2 agonist (e.g. formoterol, salmeterol): 36–48 hours · ultra-long-acting beta2 agonist (e.g. vilanterol, indacaterol): 48 hours · ipratropium (e.g. Atrovent): 12 hours · long-acting anticholinergic (e.g. tiotropium): 7 days · inhaled corticosteroid and montelukast: as agreed · antihistamine (allergy medication): 3 days.
    Before an indirect test (mannitol, EVH or an exercise challenge), also note: avoid hard exercise in the last 4 hours and caffeine (coffee, tea, cola, energy drinks) on the day of the test. Neither applies before a methacholine test. If you have had an airway infection within the last two to six weeks, please call and reschedule.
  • Skin-prick test (allergy test): antihistamine (allergy medication): 3 days.
  • Bring an up-to-date medication list and any earlier lung function measurements.
  • Always bring your reliever inhaler.

Before your visit

Written by Emil Ingerslev Walsted, specialist in respiratory medicine, PhD. Last reviewed September 2026. Next scheduled review September 2027. This page is general information and does not replace a medical assessment.

Time to have your lungs tested?

Lung-function testing is part of almost every work-up at the clinic and is performed at your visit when relevant. A referral from your GP is normally required; you can also be seen as a private or insurance patient. This page is general information and does not replace a medical assessment.