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Pulmonary Function Tests

Medically reviewed by Last updated on Aug 31, 2022.

What do I need to know about pulmonary function tests (PFTs)?

PFTs measure how well your lungs work. PFTs may show the cause of breathing problems or how well treatments for a lung condition are working.

How do I prepare for PFTs?

  • Your healthcare provider will talk to you about how to prepare for these tests. You may need to stop taking certain medicines 4 to 24 hours before your tests. Your provider will tell you the medicines to take or not take on the day of your tests.
  • If you use oxygen, you may need to stop using it for a short time before you have these tests.
  • You may be told not to smoke, have caffeine, or exercise on the day of your tests.
  • If you use dentures, you may be asked to remove them for the tests.

What will happen during PFTs?

  • Spirometry measures how much air you breathe in and breathe out, and how fast you can blow air out. During this test, you will sit or stand next to a machine. A healthcare provider will place soft clips on your nose. He or she will tell you how to breathe into the machine. You will be asked to breathe normally several times. You will breathe in as deeply you can, and then breathe out forcefully for about 6 seconds. You will then be asked to breathe in deeply again. You may be given a breathing medicine during this test to see if it helps your lungs.
  • Lung diffusion capacity measures how well your lungs can move oxygen into your bloodstream. For this test, you will breathe in a gas through a tube. You will be asked to hold your breath for about 10 seconds and then breathe out.
  • Body plethysmography measures the amount of air in your lungs after you take a deep breath in. It also measures how much air stays in your lungs after you breathe out. You will sit inside a sealed box about the size of a phone booth. You will be asked to breathe into a tube that is connected to a computer. The healthcare provider will tell you how to breathe into this tube.

What are the risks of PFTs?

Deep breathing done during some tests may cause you to feel short of breath, dizzy, or lightheaded. It may also cause you to cough.

When should I seek immediate care?

  • Your shortness of breath does not get better after treatment, or it gets worse.
  • You cough up blood.

When should I call my doctor?

  • You have new or worsening symptoms.
  • You have questions or concerns about your condition or care.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.