Lung Function Tests & breathing tests

This page is designed to outline the reasons why you have been advised to have breathing tests and how to prepare for them. If your doctor suspects that you have a lung condition, they may order a number of different tests, which will be outlined in detail below. This page will also offer information and advice for patients to prepare for the test, so they know what to expect and what to ask their doctor.

What do breathing tests show?

Breathing tests may be carried out for a number of reasons and are designed to check:

  • How well you can breathe and identify any problems with the way you breathe in and out.
  • How well your lungs are functioning.
  • How well your lungs function during and after exercise.
  • How taking medication affects your lungs.
  • How your lungs function when you are asleep.

Breathing tests are not painful and you should not be worried about the tests. You will be required to exercise for the test to see how much air you can blow out, but this will only be light exercise. If you are worried about the test, talk to your doctor and they will be able to answer any questions you have and help put your mind at ease.

Types of breathing test

There are many different tests that can be carried out to test your breathing. These include:

Lung function tests

Lung function tests are carried out to evaluate the ways your lungs work. The tests are short and painless and involve blowing into a mouthpiece or tube, which is connected to a machine that will be used to determine how well your lungs are functioning. Sometimes you may be asked to sit in a cubicle while you have the test, which allows the tester to obtain more detailed readings. If you are blowing through your nose, this may affect the result and you will be asked to wear a nose clip for the duration of the test. You will usually be asked to repeat the test several times but it should take no longer than an hour in total.

Peak flow

Peak flow is the most commonly performed breathing test and is designed to measure the speed you can blow out. The test is very simple and all you have to do is take a very deep breath in and then blow out as fast as you can. Peak flow is often used in the diagnosis of asthma.


Spirometry measures the amount of air you can breathe out in one second, which is known as FEV1. This test is used in the diagnosis of COPD (chronic obstructive pulmonary disease) and may be useful in detecting narrowing of the bronchial tubes, which makes it more difficult to breathe and is also found in people with asthma and COPD.

Blood gas tests

Blood gas tests are carried out to see if oxygen is entering the lungs and carbon dioxide is leaving the lungs in the correct way. The test involves a small device known as an oximeter, which is attached to the finger or the earlobe. The device does not take any blood but rather shows how red the blood is and therefore how much oxygen is in the blood. To measure the amount of carbon dioxide, a sample of blood will be taken from an artery in the arm or sometimes from the earlobe, which is less painful. If you are wearing nail varnish, this may obstruct the oximeter, so you may be asked to remove it in one finger nail.

Exercise tests

Exercise has an effect on the way the lungs work because people need to breathe more when they are exercising. In order to check how well your lungs work during exercise you will be asked to do some light exercises, which may include:

  • Walking for around 6 minutes: this can go at your own pace and take breaks if necessary.
  • Doing a walking shuttle test: this involves walking a distance of around 10 metres in shuttles in an allotted time. As the test progresses the time allotted to complete the shuttle decreases, meaning you have to walk faster.
  • Walking on a treadmill: as you walk, the actions of your heart and lungs will be monitored and evaluated.
  • Exercise bike: you will be asked to cycle while wearing a mouthpiece and your breathing will be measured while you cycle.

Treatment reversibility test

This test involves a spirometry test followed by breathing into a machine called a bronchodilator; bronchodilator machines are designed to widen the airways to make it easier to breathe. Medication will be given and another spirometry test will be done to check if the results have improved. If you have asthma the results will improve but the results are likely to stay the same if you have COPD. The test is used to determine whether a patient has asthma or COPD, decide which course of treatment is best for the patient and see how the lungs respond to medication. Before you have the test you will be advised to avoid taking your inhaler for a period of time.

Tests during sleep

Some people find it difficult to breathe while they are asleep, so doctors may carry out tests to see if they can identify a cause. One of the most common reasons for breathing difficulties during sleep is sleep apnoea, a condition which causes many people to stop breathing, snore and wake up several times during the night. In severe cases it can be fatal. If your doctor suspects that you may have sleep apnoea, you will be asked to wear an oximeter during the night, which will measure your blood oxygen levels while you sleep and show whether levels fall during the night. If the test suggests that you have sleep apnoea, you will be advised to have further tests in hospital. Doctors will monitor you overnight to see how you breathe during sleep, check your blood oxygen levels and check your breathing patterns. You will not feel any pain or discomfort during the tests.

Additional tests

In addition to the tests mentioned above, further tests may be required. These include tests to see whether you would benefit from oxygen at home and tests to see if you are safe to fly.

Oxygen at home

If your breathing is very bad you may need oxygen at home. If your lungs have failed, this means that only a low level of oxygen is getting into the bloodstream and you may not be able to expel carbon dioxide properly. Oxygen is delivered from a machine called an oxygen concentrator, which is usually used for at least 15 hours per day every day. To determine whether you need at home oxygen your doctors will carry out blood gas tests on two separate occasions, usually between 2 and 3 weeks apart. Your doctor will monitor your condition to check that you are getting enough oxygen.

Fit to fly test

If you have a lung condition, this may increase your risk of problems during a flight so your doctor will carry out tests to check that you are well enough to fly. During the test you will be asked to breathe through a mask, which will have a lower concentration of oxygen than normal, to mimic the level on a plane and doctors will see if your lungs can cope with the decreased level of oxygen. If there is not enough oxygen in your blood, the doctor will increase the level of oxygen in the mask until your blood oxygen levels are stable and healthy. You will then be given a letter signed by your doctor to say that you require oxygen during the flight. If this is the case you will need to check with the airline so they can provide oxygen for you; however, in some case there may be an additional charge.

Home nebuliser

Some people require a nebuliser to help them breathe more easily. The nebuliser gives you a puff of medication, which is used to dilate the airways and it is equivalent to taking 6 puffs of an inhaler. If your doctor thinks you may benefit from having a nebuliser, you will be advised to attend a specialist clinic. Nebulisers are not widely available on the NHS but can be bought for between £60 and £120.

Gas transfer test

The gas transfer test shows how well oxygen is entering the lungs and carbon dioxide is coming out of the lungs. The test is very simple: you will be asked to hold your breath and then breathe into a mouthpiece. You should not smoke for at least 24 hours before this test.

Lung volume test

This test involves breathing normally for around 15 minutes. A machine will monitor your breathing during this time and your lung volume will be measured.

What should I ask before my test?

It is normal to have questions before you have a test, so do not feel embarrassed to ask your doctor. Here are some ideas for questions you may want to ask:

  • Why do I need the test?
  • What will the test show?
  • Will I feel any pain?
  • Where will the test take place?
  • How long will the test take?
  • Will I be able to drive after the test?
  • Do I need to follow any instructions before the test?
  • When will I get my results?
  • How can I get my results?
  • What happens next?
  • Will I have to make an appointment or will my GP do it for me?
  • Is there somebody I can talk to about my results?

Before the test

For some tests you will need to follow instructions so that your results are as accurate as possible. Your doctor will explain what you need to do before the test and a letter sent to you by the hospital will also contain any relevant information about preparing for the test. You may be advised to avoid smoking, taking certain medications and drinking for a period of time before your test. Also, it is best to wear loose, comfortable clothing when you have your tests. If you have any questions or queries about preparing for the tests, contact your doctor.

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