Lung Function Tests

Last Updated 05/07/2020

Authors:Said Chaaban, MD; Ellen Becker, PhD, RRT, RPFT, AE-C, FAARC; De De Gardner, DrPH, RRT, FCCP; Mary Hart, RRT, MS, FCCP

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About Lung Function Tests

Lung 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 chronic obstructive pulmonary disease (COPD) or asthma.

Other lung tests include:

  • Lung volume test. This test is more exact than spirometry and measures the volume of air in the lungs, including the air that remains at the end of a normal breath.
  • Diffusing capacity test. This test measures how easily oxygen enters the bloodstream from the lungs. 
  • Exercise testing. Exercise testing helps determine the cause 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 technologist. The technologist will ask you to use maximum effort to take a deep breath in, blow the air out, and then breathe back in as quickly as possible. The test is repeated several times to make sure the results are accurate.

On the day of your test

Follow these directions and any directions that your health care team gave you.

On the day of your test:

  • Take your daily medications prior to testing unless told otherwise.
  • Do not smoke for at least 6 hours before your test.
  • If you use a quick-reliever inhaler as needed, do not use this inhaler for 6 to 8 hours before your test, if possible.
  • Follow all instructions your health care provider gave you.

The exercise test will be performed on a bike or treadmill. Wear loose-fitting, comfortable clothing and athletic shoes. You will wear a heart monitor and blood pressure cuff 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.

Lung function test being performed
Performing a lung function test

Understanding the results

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

What are the risks?

It is important to understand and follow directions to perform a lung function test. Tell your doctor if you have had:

  • A heart attack or stroke in past 3 months
  • A large aneurysm of a major vessel
  • A major head injury
  • Recent eye surgery
  • Confusion

If you have had any of these, you may not be able to have a lung function test.

Equipment safety

Special steps are taken to avoid spreading germs between people who use the same lung function equipment. The technologist will change mouthpieces and clean the equipment between patients. Special filters are also used to prevent the spread of germs.

If you have questions about this test, ask before the test starts.