What is a Pulmonary Function Test?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 20 October 2019
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A pulmonary function test is a test which is designed to assess lung function. These tests are used for people who have suspected lung ailments, in the process of arriving at a diagnosis, and they are also utilized on patients with lung conditions to monitor lung function. Pulmonary function tests, or PSTs as they are sometimes known, are typically brief and painless, although some people feel lightheaded after testing, since the tests involve sharp inhalations and exhalations.

One of the most common pulmonary function tests is spirometry, which is designed to measure the flow of air into and out of the lungs. In this test, the patient breathes into a mouthpiece which records the passage of air through the lungs. It can be used with both forced and quiet exhalations to gather information about lung function. This pulmonary function test literally measures breath to find out how well someone's lungs are working.

In an inhalation challenge, the patient is exposed to a small amount of an allergen in the form of a fine mist, and the patient's ability to breathe is assessed. This can be used to identify potentially problematic allergens, and to rule out substances which do not result in an allergic response during the diagnosis of allergies. Patients may also be given a diffusion capacity test, in which a harmless gas is inhaled and then exhaled, with the exhaled amount being measured to determine how much gas diffused into the blood.


In a body plethysmograph test, the patient is sealed into a box which can record minute changes in air pressure to provide information about lung function. This can be used for very precise pulmonary function testing, and it can be used to test children and patients who have difficulty cooperating with routine spirometry tests.

Bloodwork can also be used as a pulmonary function test. In an arterial blood gas test, the dissolved gases in a patient's blood are tested. Patients may also be subjected to stress tests, in which they are asked to exercise while their lung function is measured, to study shortness of breath connected to exercise.

After a pulmonary function test has been performed, a doctor can use the data to manage lung disease, or to diagnose a pulmonary condition in a patient. Patients with chronic pulmonary conditions like asthma may be asked to go in for regular testing, to monitor their conditions so that problems can be addressed early. A pulmonary function test may also be used to determine if a breathing treatment such as pure oxygen or nebulized medication is necessary for a patient.


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