Lung Function Tests

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KEY POINTS

• Lung function tests measure how well your lungs are working. There are several different tests.
• These tests can help find lung diseases such as asthma and COPD. The tests can also help find the best treatment plan for you, and check how much better your lungs work when you are given medicine.
• Talk to your healthcare provider about what the test results mean and ask any questions you have.

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What are lung function tests?

Lung function tests measure how well your lungs are working. There are several different tests. For example:

• Spirometry measures how much and how fast air can move out of your lungs. It is the most commonly used pulmonary function test.
• Diffusing capacity tests show how well your lungs can move oxygen from the air into the bloodstream.

Why are these tests done?

Lung function tests help:

• Diagnose lung diseases such as asthma, chronic bronchitis, and emphysema
• Find the cause of shortness of breath
• Measure the effects of exposure to cigarette smoke, chemicals, coal dust, and other toxins that can damage lung function
• Measure how well the lungs are working
• Find the best treatment plan for you
• Measure how much better the lungs are working when you are given medicines for narrowed airways

These tests can help find lung disease at an early stage, before you have symptoms. If your lungs are damaged, these tests may help your healthcare provider know how much they are damaged. The tests can also help see if your breathing problems are likely to get better with the use of medicines that open up the airways.

How do I prepare for these tests?

Often no preparation is needed. If you have asthma or COPD, ask your healthcare provider if you need to stop using asthma medicine before the test. Follow your provider’s instructions about eating and not smoking for 4 to 6 hours before your test.

How are the tests done?

• Spirometry: You will breathe into a mouthpiece that is connected to an instrument called a spirometer. The spirometer measures how much air you can blow out in 1 second. You will be asked to hold the mouthpiece tightly with your lips, breathe in as much air as possible, and then blow out as hard as you can into the spirometer until your lungs feel completely empty. The amount of air you can force out in the first second is called forced expiratory volume, or FEV1. The total amount of air you can force out is called forced vital capacity.
• Diffusing capacity: You will breathe in air that has a small amount of carbon monoxide (CO) gas in it and then hold your breath for a few seconds. Then you will blow out the air as quickly as possible. The concentration of CO in the air you blow out will be measured. The difference in the amounts of CO breathed in and blown out shows how well a gas, like oxygen, can pass into the blood from your lungs.

These tests are not painful, and you will have time to rest between the different tests. The tests may be repeated 2 or more times.

Ask your healthcare provider when and how you will get your test results.

What do the test results mean?

The test results can help your healthcare provider know if your lungs are normal. If your test results are not normal, the tests can help your healthcare provider know what kind of lung disease you may have and how severe it is.

Ask your healthcare provider any questions you have about your test results.

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 healthcare provider about your result and ask questions, such as:

• If you need more tests
• What kind of treatment you might need
• What lifestyle, diet, or other changes you might need to make