Lung Function Breathing Tests

Reviewed by: HU Medical Review Board | Last reviewed: July 2021

Breathing tests play a key role in finding out if a person has chronic obstructive pulmonary disease (COPD). These tests can also be used to find out the stage of a person’s COPD. These tests are called lung function tests or pulmonary function tests.1,2

Lung function tests are used to measure how well your lungs are working. People with COPD have lungs that do not work as well as they should, so these tests give doctors the information they need to diagnose and treat COPD.1,2

Doctors often use these types of lung function tests when diagnosing COPD:2

  • Spirometry test
  • Lung volume test
  • Lung diffusion capacity test

What to expect from lung function tests

These tests are not painful or invasive. Some people may feel lightheaded afterward because of heavy breathing. The test may be repeated a few times to make sure you had an accurate reading, but overall, the process does not take long. After the test, you can go back to normal activities.2

Your doctor may give you instructions before the test such as not smoking or using a rescue inhaler in the 6 hours before the test. You may also get specific instructions depending on the other medicines you take. After the test, your results are compared to what is normal for your age, gender, or height. If your results are abnormal, it may be a sign of a breathing problem.2

Spirometry test

Spirometry is the most basic of the tests. It is also the test most commonly used to diagnose COPD. A spirometry test measures how well the lungs work while exhaling by measuring 2 things:3

  • How much air you can breathe out
  • How fast you can breathe out

During the spirometry test, you will have a clip placed on your nose, and you will be seated at a machine with a mouthpiece. You will be asked to take the biggest breath you can and then blow it out as fast as possible into the mouthpiece.3

The results of the spirometry test will show if the air leaving your lungs is obstructed. This could be a sign of COPD or some other kind of respiratory problem. If you do have COPD, the results can help figure out what stage of COPD it is.3

Lung volume test

A lung volume test is similar to a spirometry test. It is sometimes called a body plethysmography test. This test measures 2 things:4

  • The largest amount of air your lungs can take in while inhaling
  • How much air is left in your lungs after fully exhaling

During the test, you will be asked to sit in a clear, airtight box that is about the size of a phone booth. You will need to breathe in and out through a tube. The person giving you the test will measure changes in the air pressure in the box you sit in. These changes in pressure help determine the amount of air in your lungs while you breathe.4

Lung diffusion capacity test

A lung diffusion capacity test measures how good your lungs are at getting oxygen from the air you breathe into your blood. During the test, you will breathe in a small amount of a harmless gas, called a tracer gas. The concentration of that gas in the air you exhale is measured. The difference in the amount of the gas you inhaled and exhaled is calculated.4

This result shows how well your lungs can move gas into your blood. If you exhale a great deal of the tracer gas, it is a sign your lungs may not be absorbing enough oxygen. This could be a sign of COPD.4

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