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What Are Lung Function Tests and Why Are They Done?

Lung function tests (also called pulmonary function tests) include a variety of tests that check how well the lungs work. The most basic test is spirometry. This test measures the amount of air the lungs can hold. The test also measures how forcefully one can empty air from the lungs.

Spirometry is used to screen for diseases that affect lung volumes. It also is used to screen for diseases that affect the airways, such as COPD or asthma.

Lung volume testing is another commonly performed lung function test. It is more precise than spirometry and measures the volume of air in the lungs, including the air that remains at the end of a normal breath. In addition, a diffusing capacity test measures how easily oxygen enters the bloodstream. Exercise testing helps evaluate causes of shortness of breath. There are also tests to find out if asthma is present when the usual breathing test results are normal.

What to Expect

These tests are not painful. They are performed by a pulmonary function technician, who will require you to use maximal effort to blow out and breathe in air. The tests are repeated several times to make sure the results are accurate. When performing the test, keep the following in mind:

  • You should take your daily medications prior to testing unless told otherwise.
  • Do not smoke for at least six hours prior to testing.
  • If you are using a short-acting inhaler that is used only as needed, do not use for six to eight hours prior to testing, if possible.
  • Your doctor may give you other instructions regarding medications.

The exercise test will be performed on a bike or treadmill and you should plan to wear loose fitting, comfortable clothing and athletic shoes. You will be attached to a heart monitor and blood pressure machine to monitor your vital signs during the test. You will be given additional instructions about how to prepare for this test at the time it is ordered.

Understanding the Results

After the test, you can return to your normal daily activities. Normal values are calculated based on age, height and gender. If a value is abnormal, a lung problem may be present. Sometimes a patient with normal lungs may have a breathing test value that is abnormal. Your doctor will explain what your test results mean.

What Are the Risks?

You need to understand and follow directions to perform a lung function test. Exercise testing should not be done in those who have had:

  • A heart attack or stroke in past three months
  • A large aneurysm of a major vessel
  • A major head injury
  • Recent eye surgery
  • Confusion 

Special steps are taken to avoid spreading germs between patients who use the same lung function equipment. The technician will change mouthpieces and other equipment between patients. Special filters are also used to prevent the spread of germs. Be sure to ask questions before the test is started.

Page last updated: May 27, 2020

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