Lung function tests

Lung function tests measure how much air your lungs hold and how quickly your lungs can move the air in and out. Spirometry is often the first lung function test that is done. You may also have other tests, such as gas diffusion tests, body plethysmography, inhalation challenge tests, and exercise stress tests. Your doctor will explain which tests you need.

These tests check how well your lungs work. They may also be called pulmonary function tests, or PFTs.

Lung function tests are done to:

• Find the cause of breathing problems.
• Find certain lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD).
• Check a person's lung function before surgery.
• Check the lungs of someone who is regularly exposed to chemicals or other things that can damage the lungs.
• Check how well treatments for lung diseases are working.

What happens during the test depends on the type of test you have.

For most tests, you will wear a nose clip. This is to make sure that no air passes in or out of your nose during the test. You then breathe into a mouthpiece attached to a recording device.

• For some tests, you breathe in and out as deeply and as fast as you can.
• You may repeat some tests after you inhale a medicine that expands your airways.
• You may breathe certain gases, such as 100% oxygen or a mixture of helium and air.
• For body plethysmography, you sit inside a small booth with windows. The booth measures pressure changes that occur as you breathe.

The therapist may urge you to breathe deeply during some of the tests to get the best results.

You may have a blood test to check the oxygen and carbon dioxide levels in your blood.

• Let your doctor know if your child takes medicines for a lung problem. Your child may need to stop some of them before the tests.
• Have your child wear loose clothing that does not restrict breathing.
• Don't let your child eat a large meal just before the test. A full stomach may keep your child's lungs from fully expanding.
• For 6 hours before the test, do not let your child exercise hard.

Normal

Results are in the normal range for a person with healthy lungs.

The normal range is just a guide. Some test values vary by things like age and height. Your doctor will also look at your results based on your symptoms, health, and other factors. A value that isn't in the normal range may still be normal for you.

Abnormal

Test results are outside of the normal range for a person with healthy lungs. This may be a sign of lung disease. Many health conditions can change how well your lungs are working. And exposure to certain things, such as smoke or chemical fumes, can also affect how well your lungs are working. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.