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Your lung function test appointment

Lung function testing for patients with breathing problems

How do I get an appointment?

You are referred for lung function tests after you have seen a doctor or consultant from our hospitals.

  • Changing or cancelling your appointment

    If you need to change or cancel your appointment, please tell us as soon as possible by calling 020 7188 7188 ext 55676 or 020 7188 5822. Please contact us if you are going to be late for your appointment as it may not be possible for us to see you if you are more than 15 minutes late.

  • Before your appointment

    If you use an inhaler:

    • please do not use Salbutamol/Ventolin and Terbutaline/Bricanyl for six hours prior to your appointment.

    Refrain from using long acting bronchodilators such as Serevent, Symbicort, Seretide, Flutiform for at least 24 hours prior to your appointment.

    • Do not use Spiriva for 24 hours prior to your appointment.

    Prior to your test it is important that you refrain from the following as they may impact on your test results:

    • smoking for 24 hours
    • drinking alcohol four hours prior to testing
    • exercising 30 minutes prior to testing
    • eating a large meal two hours before your test
    • do not wear tight fitting clothing which can restrict your chest or abdomen.

    Please inform us prior to your appointment if you have experienced any of the following in the six weeks before your appointment as it may be necessary to rearrange your appointment:

    • a recent heart attack
    • coughing up blood, within three days of appointment
    • recent collapsed lung or blood clot in the lung
    • recent eye, abdominal (stomach) or chest surgery
    • if you have had a chest, stomach or cerebral (brain) aneurysm (bulge in blood vessel)
    • if you currently have a chest infection.

    Additional instructions for specific tests

    For patients undertaking the mannitol challenge, exercise test and six minute walk test, or skin prick allergy test there are some additional instructions.

    Exercise test and six minute walk test
    Please wear comfortable clothes and shoes and do not wear nail polish on the day of testing.
    Skin prick test
    Refrain from using antihistamine tablets and nasal sprays such as (Zyrtec, Telfast, Claratyne) three full days prior to testing.
    Manitol Challenge
    Please check the following table to find out what medications need to be withheld before performing this test. Failure to withhold some medications may affect the results of challenge.
    Medications to withhold before the Mannitol Challenge
    Time to withholdMedication
     6-8 hours inhaled non-steroidal anti-inflammatory agents (eg sodium cromoglycate, nedocromil sodium)
     8 hours short-acting beta 2 agonists (eg salbutamol, terbutaline)
     12 hours inhaled corticosteroids (eg beclomethasone, budesonide)
     12 hours ipratropium bromide
     24 hours inhaled corticosteroids plus long-acting beta agonists (eg fluticasone and salmeterol; budesonide and formoterol)
     24 hours long acting beta 2 agonists (eg salmeterol, eformoterol)
     24 hours theophylline
     72 hours tiotropium bromide
     72 hours antihistamine tablets and nasal sprays (eg cetirizine, fexofenadine and lorotadine)
     4 days leukotriene-receptor antagonists (eg montelukast)
  • What to expect at your appointment

    During your appointment with us, you will be required to perform a number of lung function tests (breathing tests) which are designed to determine how well you move air in and out of your lungs and how well oxygen enters your body.

    Common pulmonary function tests


    This test measures how much air you can empty out of your lungs. This test is done by having you take a deep breath in, followed by a maximal blow out as fast as you can; you keep blowing out until all the air is expired. You will be required to blow into a tube connected to a machine (spirometer). To get the best results, the test is repeated at least three times. There is a rest period between each test.

    You may be required to repeat this test 20 minutes after taking an inhaler (bronchodilator) to see how much benefit the inhaler gives.

    Gas diffusion tests

    A gas diffusion test is performed to see how well you are able to move the oxygen (that you breathe in from the air) from your lungs into your blood supply. This test will involve you breathing in some gas. During this test you will be required to breathe into a machine whilst connected to a mouthpiece. The test procedure will require you to breathe normally on the mouthpiece, then take a deep breath in and gently blow out as far as possible; you will then be required to take a quick deep breath in as far as you can, hold your breath for 10 seconds, and to then breathe out as directed.

    Static lung volumes (helium dilution or body plethysmography)

    This test measures how much air you have left in your lungs after blowing all the way out. There are two different methods that can be used.

    • Helium dilution will involve breathing a gas mixture (helium and oxygen). You will breath normally into a mouthpiece connected to a machine for approximately five minutes. Once the helium concentration becomes stable you will be asked to take a deep breath in and to then blow out as far as possible before breathing back in again.
    • Body plethysmography will require you to sit in a booth similar to a phone box, the door will be closed and you will be attached to the mouthpiece. You will then be required to place your hand on your cheeks and breathe normally. At various stages during the test a shutter will briefly block the mouthpiece and various pressure measurements will be taken as you continue to breathe normally against the shutter.

    How long will your tests take

    Depending on which tests the doctor has requested for you to have, it will take between 30-60 minutes for us to complete your testing.

  • Additional tests

    Some patients will be required to perform the following tests:

    Mannitol challenge

    The Mannitol Challenge is designed to determine if you have over sensitive airways. Over sensitivity can be caused by inflammation and is a feature of asthma. When Mannitol is inhaled by people with over sensitive airways their airways will narrow. We will use a simple breathing test to monitor this.

    The process of the Mannitol challenge will involve you inhaling a powder form of Mannitol in increasing doses from an inhaler. You will then perform a breathing test one minute after each dose until a change is observed or the test is completed.

    You may experience increased coughing, wheeziness and breathlessness during this test, but an inhaler can be given at the end to relieve any symptoms.

    Six minute walking test

    This test will require you to walk for six minutes up and down a corridor whilst your oxygen saturation levels and heart rate are monitored via a finger probe. During the test you are able to rest if required.

    Skin prick allergy test

    This test is carried out to see if you are allergic to various airborne allergens (eg grass pollen, animal hair etc). During this test a grid will be drawn on your arm, and the allergen solutions placed within that grid. A lancet will be used to irritate the top layer of skin (the skin will not break). You will then be required to wait for 15 minutes to see if the allergens cause a reaction.

    Fitness to fly test

    This test is carried out to see if you require oxygen during a plane flight. When flying the air pressure in the aircraft is lower than at ground level. As a result, oxygen levels in your blood will fall, which can make some people feel breathless. This can be a problem for people who already have low blood oxygen levels due to a lung condition, with the extra reduction causing discomfort.

    During the Fitness to Fly test you will breathe Nitrogen gas for 20 minutes whilst your oxygen saturation levels are monitored; this will mimic flying at altitude. If your Oxygen saturation level drops below 85% then you will be given increasing amounts of oxygen to determine how much oxygen you will require during your flight.

    CPET (exercise bike test)

    The CPET test is a measurement of the heart and lungs during exercise and is carried out to assess your exercise capacity. It is used to help investigate breathlessness as well as estimate the risk for patients undergoing surgery.

    During the test you will be seated on an exercise bike with ECG electrodes attached to your chest to monitor your heart. You will have a facemask attached to monitor your breathing, a blood pressure cuff placed around your arm and a finger probe to monitor oxygen saturation levels.

    After some resting data has been collected you will be required to cycle at a low resistance which will gradually increase as the test goes on until you no longer feel that you can cycle or until you are unable to turn the pedals at a specific rate. Once the test is completed there will be a recovery period to see how long it takes for your heart rate and breathing to return to pre exercise values.  

    How long will your tests take

    Depending on which tests the doctor has requested for you to have it will take between 30-60 minutes for us to complete your testing.

Useful links



Guy's Hospital
020 7188 5836

St Thomas’ Hospital
020 7188 5813