Lung function

Find out how to contact your lung function service.

What is lung function?

Lung function refers to how well a person's lungs and respiratory system are working. We use lung function tests as a way to assess diagnose breathing problems, such as shortness of breath. This is done by looking at different aspects of the lung, including how well and how much you can breathe in and out, how large your lungs are and how well your lungs are able to exchange oxygen.

We might ask to you to take a lung function test if you are suffering from shortness of breath.

What do you look for in a lung function test?

We can use a number of lung function tests to identify whether you have lung problems. We measure:

  • How much air you can take into your lungs. This amount is compared with that of other people your age, height, and sex. This allows your doctor to see whether you're in the normal range.
  • How much air you can blow out of your lungs and how fast you can do it.
  • How well your lungs deliver oxygen to your blood.
  • The strength of your breathing muscles.

Doctors can use the results of these tests to determine whether your lungs are functioning optimally and within the limits expected and to help diagnose conditions such as asthma, pulmonary fibrosis (scarring of the lung tissue), and COPD (chronic obstructive pulmonary disease).

Read about respiratory diagnostic tests

Lung function tests are usually painless and rarely cause side effects. You may feel some discomfort during a capillary blood gas test when the blood sample is taken. If you are unsure of your fitness to perform the tests, ie if you are unwell with a virus or chest infection, feeling sick or have had recent surgery please contact the department to discuss whether your appointment may need to be rescheduled or cancelled.

Our specialist tests: diagnosing lung problems

We also provide a number of specialist tests. These include hypoxic challenge testing (also known as a “fitness to fly” assessment), skin allergen testing, six minute walk test, bronchial challenge testing and sleep studies.

Additional specialist tests are performed at the Royal Free Hospital. These include airways resistance using plethysmography, capillary ear lobe blood gases including long term oxygen (LTOT) assessments, mouth and nasal pressures to measure the strength of the respiratory muscles, anatomical shunts and overnight transcutaneous carbon dioxide (tcCO2) monitoring.

Which tests will I have?

You will be informed by letter and patient leaflet as to which tests your doctor would like you to have and which department you will need to attend to have the test(s) performed. If you are unsure of either of these things please contact us.


E referral CDC Lung Function (word doc)