Preparing for a Pulmonary Function Test

pulmonary function testPreparing for any medical test can be nerve-wracking if you do not know what to expect. As such, it is a good idea to educate yourself about the test, as well as how to prepare for it, so you are ready when the time comes. Here is what you need to know about pulmonary function tests and how to prepare yourself before the test itself.

What Is a Pulmonary Function Test?

A pulmonary function test (PFT) is a noninvasive test that evaluates how well your lungs are working by measuring the amount of air in your lungs, as well as how effectively your lungs move air in and out. If you are having breathing problems, asthma or other chronic lung conditions, your health care provider may request a PFT test in order to measure the severity of your lung problems, diagnose lung disease or COPD or ascertain whether a specific treatment you have been on is working.

Depending on what your health care provider needs to find out, you may be asked to take a spirometry test, which involves breathing into a mouthpiece attached to a small electronic machine, or a plethysmography test, which involves sitting or standing inside an air-tight box the size of a small, square telephone booth. You may also require a blood-gas test or a diffusion capacity test (DLCO) to test how well your lungs transfer gasses. These tests measure how well your lungs are functioning by measuring your lungs’ volume, capacity, gas exchange and rates of flow.

Different Pulmonary Function Test Measures

A PFT test can measure a variety of lung volume values, offering your doctor a lot of helpful information about your lung function and condition. Your doctor will want to gather plenty of other health information first, however, as these test results must be interpreted based on your medical history and current physical health. Once all aspects of your health and your PFT test results are taken into account, your doctor can learn about your overall respiratory health and the progression of any lung disease, as well as get a better idea of how certain treatments and medications are working for you.[1][2] 

Here are the lung volume measures your doctor may want more information on, as well as what each of the lung volume measures means. In some cases, different measurements will be used to calculate other measurements for a full picture of your respiratory function and health. 

Lung Volume Measures:[1][2]

  • Expiratory reserve volume (ERV): This is the volume of air that you can exhale after the exhalation of a normal breath, or the tidal volume.
  • Forced expiratory flow (FEF): This is your average rate of flow during the middle half of the FVC test.
  • Forced expiratory volume (FEV): This is the amount of air you exhale during the first three seconds of the FVC test.
  • Forced vital capacity (FVC): This is the amount of air you can exhale forcefully and quickly after inhaling as much as you can.
  • Functional residual capacity (FRC): This is the volume of air left in your lungs following exhalation of a normal breath, or your tidal volume (ERV + RV).
  • Inspiratory reserve volume (IRV): This is the volume of air that you can inhale over and above a normal breath, or your tidal volume.
  • Minute volume (MV): This is the total volume of air you exhale per minute.
  • Peak expiratory flow rate (PEFR): This is the fastest rate at which you can force air out of your lungs.
  • Residual volume (RV): This is the volume of air left in your lungs after your maximum exhalation.
  • Tidal volume (TV): This is the volume of air inhaled or exhaled while breathing normally when you are at rest.
  • Total lung capacity (TLC): This is the total volume of air your lungs hold when you have inhaled as much air as possible (IRV + TV + ERV + RV).
  • Vital capacity (VC): This is the total volume of air that you can forcefully exhale after inhaling as much as you can (IRV + TV + ERV).

Lung volume testing is typically indicated when a patient has an abnormal spirometry result, often indicating lung disease. Additional PFT testing is then ordered to confirm the presence of the suspected lung disease.[3]  

Normal values for your PFT test will vary, and are based on the average for someone of your same age, height, race and sex. Once conducted, your doctor will take all of these variables into account to determine whether you fall into a normal result range. If you are given multiple PFT tests, your results will also be compared to your previous test results.[1] 

Keep in mind that your lung capacity will decline somewhat as you get older. Lungs mature between the ages of 20 and 25. A healthy adult has a total lung capacity (TLC) of about six liters, which is comparable to about three large bottles of soda pop. However, around the age of 35, lung function begins to decrease slightly naturally, so some reduction in lung volume is to be expected even for healthy adults.[4]  

It is also important to note that variations in your results may be due to different technicians.[2] As such, it may be helpful to ask about the technician’s experience level before your PFT test, just so you are aware of how much variation to expect in your results.

What to Do Before a Pulmonary Function Test

Before a PFT test, it is important to tell your doctor about any conditions, surgeries or medications that could affect your health during the test or affect the results of your test. If you have recently had eye, chest or belly surgery, you should not have a pulmonary function test until you are fully recovered. If you have recently had chest pain, a heart attack or any other heart condition, you should wait to conduct the test. Anyone with an aneurysm in the belly, brain or chest should not take this test. Patients with a cold, flu or active tuberculosis should also wait until they are feeling better before taking a PFT test. Additionally, patients who are pregnant, using bronchodilators or pain medications, or experiencing excessive tiredness or stomach bloating that could affect their ability to properly take a deep breath may have PFT results that are less accurate.

Once your doctor is aware of any conditions that could affect your health or the accuracy of your PFT test, wait to be cleared for the test. Once you are cleared, it is time to prepare for taking the test. Your health care provider will have specific instructions that are unique to your situation, but in general, you should:

  • Bring a list of all supplements, medications and vitamins you are taking
  • Stop taking certain medicines, as directed, before the procedure
  • Refrain from using your bronchodilator, as directed, before the PFT test
  • Avoid caffeine before the test
  • Avoid eating a heavy meal before the test
  • Not smoke for several hours, or as directed, before the PFT test
  • Avoid exercising strenuously for several hours before the test
  • Wear loose, comfortable clothing for the test
  • Relax as much as possible
  • Follow any other directions provided by your health care provider

In addition, you will be asked to sign a consent form to provide permission for the PFT test before it is conducted .

What Happens During a Pulmonary Function Test

PFT tests are usually outpatient procedures, though they may be performed during a hospital stay. Here is what happens during each of the tests:

  • Spirometry: A spirometry test measures the amount of air you are able to inhale and exhale, and how quickly you exhale air from your lungs. During the test, you will place a clip over your nose to prevent exhaling through your nose, and you will form a tight seal over the sterile mouthpiece that is attached to a small machine (the spirometer). You will then breathe through the mouthpiece as directed, as it measures and records your test results. You may also do spirometry tests that measure how effectively a certain medication is working for you. In this case, you will take the test as usual, then take your breathing treatment or medication, then do another spirometry test to see how well the treatment aids your lung function.
  • Plethysmography: A plethysmography test measures your total lung capacity. The body plethysmography test is performed in an acrylic, airtight booth where you will sit and breathe into the same mouthpiece used for a spirometry test, but the door to the transparent box will be closed for a full minute. Alternatively, you may perform a nitrogen washout, which will involve inhaling concentrated oxygen for a short period of time, with the door to the booth open, to determine your lung volume capacity.
  • Diffusion Capacity: A diffusion capacity test, or DLCO, tests your lungs to see how well the alveoli and pulmonary capillary blood transfer gases between them. You will use the same mouthpiece as used in the other tests to breathe in specific gases during the test.
  • Pulse oximeter test and/or an arterial blood gas test: These tests measure the amount of carbon dioxide and oxygen in your blood. A pulse oximeter can do so without a needle, while the arterial blood gas (ABG) requires drawing blood from an artery as you rest. These measurements can also help doctors determine how well your lungs are functioning and whether current treatments are working for you.

In all cases, you will be asked to wear unrestrictive clothing and jewelry. You will keep your dentures in place if you wear them, and you will be asked to empty your bladder before taking the test. During the test, remain as relaxed as you can. Your health care providers will watch for difficulty breathing, dizziness and other problems during and after the test. Following each test, you will be given an opportunity to rest and recover, particularly if you already struggle with breathing.

Preparing for Pulmonary Function Tests: Frequently Asked Questions

As you prepare for your PFT test, review these FAQs to make sure you are ready for your test and know what to expect when you go in for it.

  • Can I eat or drink before a pulmonary function test?

    You can! Just do not eat a large meal before testing since a full stomach can get in the way of your lungs inhaling to their fullest capacity. You will also want to avoid foods and drinks containing caffeine as they can dilate your airways and affect your test results.

  • What should you not do before a pulmonary function test?

    Avoid smoking and exercising strenuously before a PFT test, as well as avoiding caffeine or eating a heavy meal. You may need to refrain from taking certain medications, too, as directed by your health care provider.

  • What are the uses of pulmonary function tests (PFT) ?

    PFT tests assess how well your lungs are functioning and moving air, as well as helping to assess and diagnose certain breathing conditions like:

    • Allergies
    • Asbestosis
    • Asthma
    • Bronchiectasis
    • Chronic bronchitis
    • COPD
    • Lung cancer
    • Lung fibrosis
    • Pulmonary tumors
    • Respiratory infections
    • Sarcoidosis
    • Scleroderma
    • Other breathing conditions
  • Does anything make a PFT test less accurate?

    Certain things can affect the accuracy of a pulmonary function test, including:

      • Bloating in the abdomen that affects your ability to take in a full, deep breath
      • Bronchodilators
      • Congestion
      • Fatigue
      • Pain medications
      • Patient effort and cooperation[1]

How long does it take to get results from a pulmonary function test?

In most cases, the test itself will take less than an hour to complete, depending on which tests your health care provider is administering to you. Sometimes, your health care provider is able to review the results with you as soon as the tests are finished. However, you may need to wait a few days for the full test results to come in, particularly if a blood test is involved.

A PFT test provides vital information to your health care provider about the health and function of your lungs. For patients receiving treatment for lung conditions, a pulmonary function test can tell health care providers how effective your current treatments are for your breathing. If you or a loved one are having difficulty breathing, or suspect that you have a lung condition or need additional treatment or medication, talk to your doctor about getting a PFT test today.


[1] “Pulmonary Function Tests.” Pulmonary Function Tests | Johns Hopkins Medicine, Johns Hopkins Medicine, Accessed 15 May 2020,

[2] “Iowa Head and Neck Protocols.” Pulmonary Function Testing (PFT) Made Simple | Iowa Head and Neck Protocols, University of Iowa Health Care, 5 Nov. 2018,

[3] Delgado, Benjamin J., and Tushar Bajaj. “Physiology, Lung Capacity.” StatPearls [Internet]., U.S. National Library of Medicine, 16 Apr. 2019,

[4] “Lung Capacity and Aging.” American Lung Association, American Lung Association, 11 Mar. 2020,

Additional sources not cited in blog:

Lutfi, Mohamed Faisal. “The Physiological Basis and Clinical Significance of Lung Volume Measurements.” Multidisciplinary Respiratory Medicine, BioMed Central, 9 Feb. 2017,

Martel, Janelle. “Pulmonary Function Test.” Healthline, Healthline, 13 Dec. 2017,

“Pulmonary Function Testing.” Kamelhar-Teller Pulmonology, Kamelhar Pulmonary Medicine, Accessed May 2020,

“Pulmonary Function Tests.” Pulmonary Function Tests | Johns Hopkins Medicine, Johns Hopkins Medicine, Accessed May 2020,,p07759.

“Respiratory & Pulmonary Care: Tupelo.” North Mississippi Health Services, North Mississippi Health Services, Accessed May 2020,


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