Pulmonary function tests (PFTs) are a group of tests to assess breathing. They can show how well your lungs are working. PFTs may measure:

  • How much air you can blow out
  • How much air your lungs can hold at different times during the breathing cycle
  • How fast you are blowing air out
  • How well gas is being transferred from your lungs into your blood
Respiratory System
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Reasons for Test

PFTs may be used to help diagnose lung conditions or diseases, such as:

These tests may also be done to:

  • Determine how well a treatment is working
  • Evaluate symptoms, such as coughing , wheezing, and trouble breathing
  • Evaluate your lung function before or after a surgery
  • Measure how much a lung problem or muscle weakness is affecting you

Possible Complications

There are no major complications linked to this procedure.

What to Expect

Prior to Test

  • Review your medications with your doctor. You may need to stop taking some before testing.
  • Do not eat, smoke, or exercise 4-8 hours before testing.
  • Wear loose-fitting clothing.

Description of Test

Most tests will require you to breathe into a mouthpiece. The mouthpiece may be attached to a simple handheld device or be part of a larger machine. Examples of devices are:

  • Spirometer
  • Peak flow meter

You may be asked to breathe in and out in different patterns and speeds. You will rest between tests.

Tell the technician right away if you have breathing problems, pain, or dizziness during the test.

Peak Flow Meter
Lung test peak flow meter
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Other steps that may be needed include:

  • A brief period of exercise before the test.
  • The level of oxygen in your blood may be measured during the test. This can be done with a small clip on your finger.
  • A special chemical called methacholine may be given during the test. It will be given as a vapor for you to breathe in. The vapor will make your airways spasm if you have asthma. This is only done under close and careful supervision. It may help if asthma signs were not present in basic tests.

You may be asked to breathe in small amount of carbon monoxide for 1 minute. It will be followed to see how much gets into your blood. This will suggest how well oxygen is getting into your blood.

After Test

Rest until you feel able to leave. You may be given treatment if testing has caused wheezing, coughing, and/or problems breathing.

How Long Will It Take?

20-45 minutes

Will It Hurt?

The test does not hurt. You may feel some symptoms during or right after testing.


Your doctor will compare the results of your tests with normal values. Your age, gender, and height, or previous test results will be considered as well. Your doctor will discuss the results with you. If needed, further testing or treatment plans will be made.

Call Your Doctor

After the test, call your doctor if any of the following occurs:

  • Headaches, nausea, muscle aches, lightheadedness, or general ill feeling
  • Shortness of breath or difficulty breathing
  • Wheezing or persistent coughing
  • Chest pain

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