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What are pulmonary function tests (PFTs)? 

Pulmonary function tests (PFTs) are a group of tests that help healthcare providers to know the efficiency of your lungs. 

Some of these parameters are as follows:

  • Total lung capacity (TLC): It is the overall volume of lungs when filled the most with air. 
  • Tidal volume: It is the volume of air that is either breathed in or out at once. 
  • Vital capacity: It is the total volume of air that can be exhaled after fully breathing in. 
  • Residual volume (RV): It is the volume of air left after exhaling most of the air. 
  • Minute volume: It is the total air that is breathed out in a minute. 
  • Functional residual capacity (FRC): It is the quantity of air left in lungs after breathing out fully. 
  • Forced vital capacity (FVC): It is the volume of air, which is exhaled forcefully and quickly after fully breathing in. Using this parameter, we can detect:
    • Forced expiratory flow (FEF): It is the average rate of flow measured in the middle of the FVC test. 
    • Forced expiratory volume (FEV): It is the amount of air exhaled during the first three seconds of the FVC test. 
  • Peak expiratory flow rate: The fastest rate of forcefully exhaling air out of the lungs.
  • Diffusion capacity of lung for carbon monoxide (DLCO): The gas carbon monoxide is to be inhaled in this test - this gas follows the same pathway as oxygen but has a high affinity for haemoglobin. The difference in the quantity of gas inhaled and respired gives the diffusion of gas through the lungs into the blood.

This test is performed in two ways:

  • Spirometry: In this test, a mouthpiece is attached to a device called spirometer is used to measure the airflow in your lungs (how much air you breathe in and out).  
  • Plethysmography: An airtight box that looks like a phone booth is used to perform plethysmography. This test helps determine lung volume by reading the changes in pressure inside a box while you inhale into it.
  1. What are the other tests that can be done with pulmonary function test (PFT)?
  2. Who cannot have a pulmonary function test (PFT)?
  3. Why is pulmonary function test (PFT) done?
  4. How should I prepare for pulmonary function test (PFT)?
  5. What is the procedure for a pulmonary function test (PFT)?
  6. How will a pulmonary function test (PFT) feel like?
  7. What do the results of a pulmonary function test (PFT) mean?
  8. What are the risks and benefits of pulmonary function test (PFT)?
  9. What happens after pulmonary function test (PFT)?

For a lung disorder, the other tests done with PFT include the following:

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

Individuals with the following conditions should avoid this test:

Your healthcare provider may order this test to detect and diagnose lung disorders including infections, allergies, inflammation, tumours etc. 

The following are some symptoms that you may have a lung problem:

Doctors may also order this test as a routine check-up or for employees working in graphite or coal mines. Additionally, a pulmonary function test is done to check the possible effect of certain medications like bronchodilators.

The following are some preparations that are needed before pulmonary function tests:

  • You will have to sign a consent form before the test.
  • Do not consume a heavy meal or smoke for four to six hours before the test.
  • Inform your doctor about any medication that you take. This includes prescribed or non-prescribed medicines, herbs, vitamins and supplements. Your doctor may advise you to skip bronchodilator or inhalation medicines before the test.
  • Wear loose and comfortable clothes and remove all the jewellery before the test.

The following procedure is performed for pulmonary function tests:


  • Your healthcare practitioner will ask you to sit on a chair. 
  • He/she place a soft clip on your nose. Thus, allowing inhalation through the mouth only. 
  • Thereafter, the doctor will put a sterile mouthpiece of a spirometer in your mouth and will instruct you to breathe in and out. 

In some cases, bronchodilators (medications to dilate your airways) are given, and the test is repeated after a few minutes to check for its effect.


  • You will be asked to sit in a phone booth like see-through box.
  • The doctor will give you a clip to put on your nose so you breathe through your mouth only.
  • Next, you will be asked to breathe in and out in a mouthpiece.

You may have temporary dizziness or trouble breathing during the test. Some people feel claustrophobic (fear of enclosed spaces) while some also cough during the test.

Normal results:

Normal results for pulmonary function tests are based on your age, sex and height and may vary among laboratories.

The normal values for different parameters of PFT (in percentage) are as follows:

PFT Normal value
FEV  80% to 120%
FVC 80% to 120%
TLC  80% to 120%
FRC 75% to 120%
RV 75% to 120%
DLCO >60% to <120%

Abnormal results:

An abnormal result indicates lung or chest diseases for example:

PFT is a safe and non-invasive test.

The risks of PFT would be that some individuals may experience an asthma attack or collapsed lungs during the test.

Some people may feel exhausted after the test. If such is the case, your healthcare provider will advise you to rest.


  1. University of Rochester Medical Center [Internet]. University of Rochester. New York. US; Pulmonary Function Tests
  2. Scanlon PD. Respiratory function: mechanisms and testing. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 85
  3. Gold WM, Koth LL. Pulmonary function testing. In: Broaddus VC, Mason RJ, Ernst JD, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 6th ed. Philadelphia, PA: ElsevierSaunders; 2016:chap 25
  4. Putnam JB. Lung, chest wall, pleura, and mediastinum. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, eds. Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice. 20th ed. Philadelphia, PA: Elsevier; 2017:chap 57
  5. American Academy of Family Physicians [Internet]. Kansas. US; An Approach to Interpreting Spirometry
  6. Cleveland Clinic [Internet]. Ohio. US; Pulmonary function testing
  7. Centers for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Tuberculosis (TB)
  8. Cystic Fibrosis Foundation [Internet]. Maryland. US; Newborn Screening for CF
  9. MedlinePlus Medical Encyclopedia [Internet]. US National Library of Medicine. Bethesda. Maryland. USA; Alpha-1 antitrypsin deficiency
  10. American Lung Association [Internet]. Illinois. US; Learn About Asthma
  11. National heart, lung and blood institute [Internet]. National Institute of Health. US; Sarcoidosis
  12. American academy of allergy, asthma and immunology [Internet]. Wisconsin. US; Asthma statistics
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