What is a Pulmonary function test?

The Pulmonary function test (PFT) evaluates the functioning of the lungs.The results of these tests tell your physician how much air your lungs can hold, how quickly you can move air into and out of your lungs, and how well your lungs are able to use oxygen and get rid of carbon dioxide. The tests help your physician determine if you have a lung disease, help provide a measure of how significant your lung disease is, and can show how well the treatment for your lung disease is working.

How is a pulmonary function test done?

Pulmonary function testing is usually done by a certified Pulmonologist. For most pulmonary function tests, you will be asked to wear a nose clip to make sure that no air passes through your nose during the test. You will be asked to breathe into a mouthpiece that is connected to a machine called a spirometer. The doctor may encourage you to breathe deeply during parts of the test to get the best results. Following all of the doctor's instructions will help provide the most accurate results.

How do you prepare for the PFT?

  • You should not eat a heavy meal just before this test.
  • You should not smoke for six hours before the test.
  • You should not exercise vigorously for six hours before the test.
  • On the day of the test, avoid food or drinks that have caffeine.
  • On the day of the test, wear loose clothing that does not restrict your breathing in any way.
  • If you have dentures, wear them during the test.

What is the purpose of a PFT?

Pulmonary function tests are performed on:

  • Evaluate if the reason for your shortness of breath is obstructive or restrictive.
  • Diagnose certain types of lung disease, such as asthma, bronchitis, and emphysema
  • Check lung function before surgery.
  • Measure progress in disease treatment.
  • Measure whether exposure to chemicals at work affects lung function.

If already diagnosed with asthma or COPD spirometry, it can determine if the current treatment is effective.

What Exactly Happens During a PFT?

You will be asked to blow (both out and in) through a mouthpiece that is tightly fitted to your mouth. The results will be recorded in the system.


Spirometry measures the function of the lungs using the most frequent measurements, which include:

  • Forced Vital Capacity (FVC) — The maximum quantity of air one can expel after taking the deepest breath.
  • Forced Expiratory Volume (FEV1) - The quantity of air that can be expelled from the lungs in the first second.
  • If the volume of air that can be expelled in the first second is low, lung disease such as asthma or COPD is suspected.

How long does the test take?

If you need spirometry testing only, it should take only 30 minutes. If you need a complete PFT, it takes about one hour.

Spirometric measures in asthma, COPD and ACOS