Pulmonary Function Tests

What Are Pulmonary Function Tests and Why Are They Done?

Pulmonary function tests (or PFTs) are also called lung function tests. If you have symptoms or risk factors for a lung disease such as COPD, pulmonary fibrosis or asthma, your healthcare provider may order PFTs, among other tests, to check how well your lungs are working. Your results will help determine if your lung function is within normal range by comparing your measured test results to predicted results generated by reference equations.

PFTs will also be ordered to monitor your diagnosed lung disease, evaluate your exposure to environmental or work-related pollutants, guide treatment options, and check how well your lungs respond to treatments.

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 will be repeated to make sure the results are accurate. Your healthcare provider or the pulmonary function technician should give you instructions. These instructions may include that you:

• continue to take your daily medications prior to testing unless told otherwise.
• not smoke for at least six hours before testing.
• not use your quick relief inhaler for six to eight hours prior to testing, if possible.
• follow additional directions about medication, what to wear, food or activity limitations.

If your healthcare provider orders cardiopulmonary exercise tests, these tests will be performed on a bike or treadmill. 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. Predicted or normal values are calculated based on age, height, and sex assigned at birth. Your healthcare provider will compare your value to the predicted value and assign you a z-score to indicate the difference.

What is a z-score?

Lung function values from a healthy population are used to understand average values for a given age, height and sex assigned at birth. A z-score estimates how close to that average your pulmonary function test results are and can be used to calculate whether your lung function is healthy. The further away your result is from the average, the more likely you have abnormal lung function. Your healthcare provider will use and track your z-score to help diagnose and monitor your lung disease.

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.

Within a few days your healthcare provider will explain what your test results mean and if further monitoring or tests are needed.

What Are the Risks?

PFTs are safe. You may feel lightheaded or dizzy from breathing so deeply. These symptoms should go away shortly after you complete your test.

You should discuss any health conditions or concerns before the PFTs.

Cardiopulmonary 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.