Pulmonary Function Testing

Pulmonary function tests (PFTs) determine how well your lungs work. They determine how much air goes into and out of your lungs, how much air goes from your lungs to your blood and how well your lungs work during exercise. Your healthcare provider will contact you a few days later with your results.


Spirometry is a type of pulmonary function testing that uses a spirometer to measure air flow and amount of air in your lungs
Pulmonary function testing measures how well your lungs work. Spirometry is a common pulmonary function test.

What are pulmonary function tests?

Pulmonary function tests (PFTs) include different kinds of breathing tests that measure how well your lungs exchange air. Your lungs help you take air in (inhale) and breathe air out (exhale).

There are many different types of PFTs. Some also measure how well your lungs absorb oxygen into your blood and how exercise affects your lungs.

PFTs are safe and don’t require a healthcare provider to put any tools or instruments inside your body (noninvasive).

Another name for pulmonary function tests is lung function tests.


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What are the types of lung function tests?

Lung function tests include:

  • Spirometry. Spirometry measures how much air you can inhale and exhale. It also estimates how much air is in your lungs.
  • Lung volumes or body plethysmography. Lung volumes or body plethysmography measure the various amounts of air that are in your lungs after different points of inhalation and exhalation.
  • Gas diffusion study. A gas diffusion study measures how much oxygen and other gases transfer from your lungs to your blood.
  • Cardiopulmonary exercise test (CPET). A CPET measures how well your heart, lungs and muscles work while you’re exercising.

What is the most common pulmonary function test?

Spirometry is the most common type of pulmonary function test.

When is pulmonary function testing performed?

Your healthcare provider may order pulmonary function tests if you have lung or airway symptoms like cough or shortness of breath, are undergoing surgery or use tobacco products (smoke). These symptoms may include:

Even if you don’t have symptoms, your healthcare provider may order a pulmonary function test as part of a routine physical examination.

PFTs also help your healthcare provider:

  • Detect narrowing in your lungs’ airways.
  • Identify early changes in your lungs’ ability to transfer oxygen to your blood.
  • Measure the effects of continued smoking on chronic pulmonary diseases.
  • Decide if medications may help improve your breathing.
  • Understand if exposure to substances in your environment has affected your lungs.
  • Determine your ability to tolerate surgery or other medical procedures.


When would pulmonary function testing be needed?

PFTs help your healthcare provider diagnose:

Who performs pulmonary function testing?

A specially trained respiratory therapist usually performs pulmonary function testing.

Test Details

How does pulmonary function testing work?

A pulmonary function test is relatively simple.

A PFT consists of a clear, airtight box, soft nose clips, a mouthpiece and a small electronic machine that measures your airflow (spirometer).


How do I prepare for a pulmonary function test?

Before your pulmonary function testing, your healthcare provider may ask you to:

  • Stop taking your breathing medicines for a short period.
  • Wear loose, comfortable clothing that doesn’t squeeze your chest.
  • Avoid any heavy exercise before your test.
  • Avoid using tobacco products before your test.

These precautions will help ensure that you get accurate results from your PFT.

Can you eat before a pulmonary function test?

You shouldn’t eat a heavy meal before your PFT.

You should also avoid any caffeine.

What should I expect on the date of pulmonary function testing?

You’ll take a PFT at a pulmonary function lab at an outpatient office or a hospital.

Before the test, your healthcare provider will record some personal information, including your:

  • Height.
  • Weight.
  • Age.
  • Race.
  • Sex.

Your healthcare provider will use this information to determine a typical value for your demographic.

What should I expect during pulmonary function testing?

After recording your information, your healthcare provider will take you to a room with PFT equipment and give you instructions according to your test.


A healthcare provider will first put soft clips on your nose. The nose clips ensure that you breathe through your mouth, not your nose.

You’ll put your lips around a mouthpiece, and the mouthpiece connects to a spirometer. The provider will then give you directions on breathing in and out.

You may take deep breaths in and out. You may also take deep breaths in and blow out as hard and as fast as you can.

Body plethysmography

A healthcare provider will put on your nose clips, and you’ll sit in the clear box. Your provider will close the door. The door remains closed for about five minutes.

Tell the healthcare provider if you’re uncomfortable in confined spaces (claustrophobic). They can help you feel more comfortable during the test.

You’ll put your lips around the mouthpiece, and the provider will give you directions on breathing in and out.

As you breathe, the spirometer will detect pressure or volume changes in the box to help measure your lung volume.

Gas diffusion study

Your healthcare provider will put on your nose clips.

You’ll put your lips around the mouthpiece, and a healthcare provider will give you directions on breathing in and out a small, safe amount of carbon monoxide.

As you breathe, the spirometer measures how much carbon monoxide you exhale. This measurement indicates how much of the gas your lungs absorbed.

Cardiopulmonary exercise test

A healthcare provider will attach you to machines that measure your heartbeat, blood pressure and blood oxygen. You’ll then walk on a treadmill or ride a stationary bicycle.

The machines will measure various aspects of your heart, lungs and muscles during the test.

How long does a pulmonary function test take?

A PFT may take between 15 and 45 minutes to complete.

Let the healthcare provider know if you get tired during your test. You can take breaks in between parts of the test.

Is pulmonary function testing painful?

No, pulmonary function testing isn’t painful.

What should I expect after pulmonary function testing?

After testing, you may restart any medicines your healthcare provider told you to stop taking. You can also return to your usual activities, including exercise.

If you felt dizzy or lightheaded during the test, the healthcare provider will monitor you until your symptoms go away and you can go home.

The healthcare provider will tell you when to expect your test results.

What are the risks of pulmonary function testing?

Pulmonary function testing is safe. But you may feel dizzy, lightheaded or tired from breathing so deeply. You may also cough from blowing into the mouthpiece or feel tired from exercising. These symptoms should go away shortly after you complete the PFT. Let the healthcare provider know if you need a break during testing.

In very rare cases, pulmonary function testing may cause a collapsed lung (pneumothorax).

A PFT can also increase your heart rate. Tell the healthcare provider if you’ve had a heart attack recently or any other heart condition.

Results and Follow-Up

What type of results will I get, and what do the results mean?

The healthcare provider will compare your score against the typical scores for your demographic. There’s a normal range expected for your age, height and sex.

What happens if you fail a pulmonary function test?

There’s no such thing as failing a PFT. If it’s abnormal, your provider will discuss additional work you may need to obtain a diagnosis and a treatment plan.

When should I know the results of my pulmonary function testing?

You should receive the results of your pulmonary function test within a few days.

When should I call my healthcare provider?

Your healthcare provider will contact you a few days after your pulmonary function test with your results. Reach out to your provider if you don’t hear from them with your results after a few days.

Based on your diagnosis, you may need regular testing to follow your condition at future visits.

A note from Cleveland Clinic

Pulmonary function testing helps your healthcare provider diagnose any conditions that affect your lungs. PFTs don’t take a long time, they aren’t painful and you should get your results in a few days.

If you notice any changes in your breathing, reach out to your healthcare provider. They may recommend a PFT to rule out a lung condition.

Medically Reviewed

Last reviewed on 10/12/2022.

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