Pulmonary Function Test

Written by Janelle Martel | Published on July 9, 2012
Medically Reviewed by George Krucik, MD on July 9, 2012

Pulmonary Function Tests

Pulmonary function tests are a group of tests that measure how well your lungs work. This includes how well you are able to breathe and how well your lungs are able to supply oxygen to the rest of your body.

Your doctor may order these tests:

  • if you are having symptoms of lung problems
  • as part of a routine physical
  • to assess how well your lungs are functioning before undergoing surgery

Pulmonary function tests are also known as PFTs, spirometry, or lung function tests.

Why This Test Is Done?

Your doctor will order this test to determine how your lungs are working. If you already have a condition that is affecting your lungs, your doctor may order this test to see if the condition is progressing or how it’s responding to treatment.

Pulmonary function tests can be used to help diagnose:

  • asthma
  • allergies
  • chronic bronchitis
  • respiratory infections
  • emphysema
  • lung fibrosis
  • bronchiectasis (a lung condition in which the airways in the lungs are stretched and widened)
  • chronic obstructive pulmonary disease (COPD)
  • asbestosis (a condition caused by exposure to asbestos)
  • sarcoidosisinflammation in the lungs, liver, lymph nodes, eyes, skin, or other tissues
  • scleroderma, a disease of the connective tissue
  • pulmonary tumor
  • lung cancer

How to Prepare for Pulmonary Function Tests

If you are on medications that open your airways, such as those used for asthma or bronchitis, your doctor may ask you to stop taking your medication before the test. Pain medications may also affect the results of the test, so you should tell your doctor about any pain medications you are on, including both over-the-counter and prescription medications.

It is important that you do not eat a large meal before testing. This is because a full stomach can prevent your lungs from inhaling fully. You should also avoid food and drinks that contain caffeine, such as chocolate, coffee, and tea, before your test. Caffeine can cause your airways to open. You will also be asked to avoid smoking and strenuous exercise before the test.

Be sure to wear loose-fitting clothing to the test. Tighter clothing may restrict your breathing. You should also avoid wearing jewelry that might affect your breathing. If you wear dentures, wear them to the test to ensure that your mouth is able to fit tightly around the mouthpiece used for the test.

What Happens During the Test


Your pulmonary function test may include spirometry, which measures the amount of air you breathe in and out. For this test, you will sit in front of a machine and be fitted with a mouthpiece. It is important that the mouthpiece fits your mouth snugly so that all the air you breathe goes into the machine. You will also be given a nose clip to wear so that you cannot exhale any air through your nose. The respiratory technologist will instruct you on how to breathe.

You may be asked to breathe normally. You also may be told to inhale and exhale as deeply and/or as rapidly as you can for several seconds. The technician may ask you to inhale a medication that opens your airways, or may have you inhale certain gases such as oxygen, helium, or carbon dioxide. You will then be asked to breathe into the machine again to see if the medication or gases affected your lung function.

You may also be asked to breathe in a “tracer gas” for one breath. This gas is able to be detected when you exhale it into the machine. This tests how well your lungs are able to transfer oxygen and carbon dioxide to and from your bloodstream.

Plethysmography Test

This test measures the volume of gas in your lungs. For this test, you will be asked to sit or stand in a small booth and breathe into a mouthpiece. The pressure in the booth will be measured to gain information about your lung volume.

What Are the Risks of Taking a Pulmonary Function Test?

Pulmonary function tests are usually safe for most people. However, because the test may require you to inhale and exhale rapidly, you may experience a feeling of lightheadness or fainting. If you feel lightheaded, inform the technician. Taking the test may also cause an asthmatic episode in individuals with asthma. In very rare cases, pulmonary function tests may cause a collapsed lung.

Individuals with certain conditions should not take a pulmonary function test, as it can cause problems. These conditions include:

  • a recent heart attack
  • heart disease
  • recent eye surgery
  • recent chest or abdominal surgery
  • respiratory infections

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