Pulmonary Function Tests

What are pulmonary function tests?
Why are these tests done?
How do I prepare for these tests?
How is the test done?
How will I get the test results?
What do the test results mean?
What if my test results are not normal?

What are pulmonary function tests?

Pulmonary function tests (PFTs) measure how well your lungs take in and exhale air and how efficiently they transfer oxygen into the blood. There are several different tests.

Spirometry measures how well the lungs exhale (breathe out).
Lung volume measures how well the lungs inhale (breathe in).
Testing the diffusion capacity of carbon monoxide (DLCO) shows how efficiently the lungs transfer oxygen from the air into the bloodstream.

Why are these tests done?

Pulmonary function tests help:

diagnose diseases of the lung such as asthma, bronchitis, and emphysema
determine the cause of shortness of breath
measure the effects of exposure to chemicals, coal dust, and other toxins on your lung function
measure the effectiveness of medicines and other treatments.

PFTs can help detect lung disease at an early stage before you have symptoms.

How do I prepare for these tests?

Eat a light meal and do not smoke for 4 to 6 hours before your test. If you have asthma, ask your health care provider if you need to stop using asthma medicine before the test.

How is the test done?

Spirometry. You breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer measures the volume of air that you can force out of your lungs in 1 second after having inhaled as much as you can. You will be asked to hold the tube of a spirometer in your mouth, inhale as much air as possible, then blow out as hard as you can into the spirometer for 1 second. The amount of air you can force out is called your forced expiratory volume, or FEV1.
Lung volume. You breathe nitrogen or helium gas through a tube for a certain amount of time. Then the concentration of the gas in a chamber attached to the tube is measured.
Diffusion capacity. You breathe carbon monoxide for a very short time (often 1 breath). The concentration of carbon monoxide in the air you exhale is then measured. The difference in the amounts of carbon monoxide inhaled and exhaled shows how quickly gas can travel from your lungs into the blood.

PFTs are painless and you will have time to rest between the different breathing measurements. The measurements may be repeated 2 or more times.

How will I get the test results?

Ask your heath care provider when and how you will get the results of your tests.

What do the test results mean?

If you do not have lung disease, you will be able to blow out 80% or more of the air in your lungs in 1 second. If you have lung disease you may be able to blow out only 20% to 40% in 1 second. With lung disease it may take you longer to get all of the air out of your lungs.

PFTs may show what type of lung disease you have.

If you have obstructive lung disease (emphysema, chronic bronchitis, or asthma), the amount of air you can exhale is decreased, but usually lung volume is normal.
If you have restrictive lung disease (such as asbestosis, pulmonary fibrosis, or sarcoidosis), the lung volume is decreased while the ability to exhale is normal.

A low diffusion capacity may indicate emphysema. It may also be caused by restrictive lung diseases that thicken the lung membrane.

What if my test results are not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your health care provider about your results and ask questions.

If your test results are not normal, ask your health care provider:

if you need additional tests
what you can do to work toward normal values
when you need to be tested again.