Key Points

• Lung function tests measure the size of your lungs, how much air you can breathe in and out, how fast you can breathe air out, and how well your lungs deliver oxygen to your blood.
• Lung function tests are used to look for the cause of breathing problems (like shortness of breath). These tests are used to check for conditions such as asthma, lung tissue scarring, and COPD (chronic obstructive pulmonary disease). They're also used to see how well treatments for breathing problems, such as asthma medicine, are working.
• Lung function tests look at how much air you can take into your lungs, 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, and how strong your breathing muscles are.
• Breathing tests include spirometry, peak flow meter, lung volume measurement, and lung diffusion capacity. Pulse oximetry and arterial blood gas tests are used to measure the oxygen level in your blood.
• People who have breathing problems, such as shortness of breath, may need lung function tests. These tests help find the cause of the breathing problems.
• If you take breathing medicines, your doctor may ask you to stop them for a short time before spirometry, a lung volume measurement test, or a lung diffusion capacity test. No special preparation is needed before pulse oximetry and arterial blood gas tests.
• For breathing tests, you will breathe through a tube that's attached to a testing machine. You may be asked to breathe normally, slowly, or rapidly. You also may be asked to inhale and then exhale a small amount of gas.
• For the tests that measure oxygen level in the blood, either a small light will be attached to your fingertip, earlobe, or toe to measure the oxygen level, or your doctor will take a small sample of your blood to measure the oxygen level.
• You can return to your normal activities and restart your medicines after lung function tests. Talk to your doctor about when you'll get the test results.
• Lung function tests can show whether you have signs of a lung or heart condition. These tests also can show how well treatments for breathing problems, such as asthma medicines, are working.
• Lung function tests are painless and rarely cause side effects. You may feel some discomfort during the arterial blood gas test when the needle is inserted into the artery.