Pulmonary function tests (PFTs) are a group of noninvasive tests that measure how well your lungs work.

A medical professional may order these tests:

  • if you’re having symptoms of a lung condition
  • if you’re regularly exposed to certain substances in the environment or your workplace
  • to monitor the course of chronic lung disease, such as asthma or chronic obstructive pulmonary disease (COPD)
  • to assess how well your lungs are working before you have surgery

In this article, we take a closer look at the different types of PFTs, when they’re used, and what conditions they may help diagnose.

A doctor will order one or more PFTs, also known as lung function tests, to determine how well you’re able to breathe and how effectively your lungs send oxygen to the rest of your body.

If you already have a condition that’s affecting your lungs, your doctor may order this test to see if the condition is progressing or how it’s responding to treatment.

PFTs can help diagnose:

PFTs can also help determine whether surgery is possible for lung cancer.

There are several different types of PFTs. Your doctor may have you do one or more of these tests depending on which health conditions they’re looking to diagnose.

Spirometry

Your PFTs may include spirometry, a painless test that can be done in a doctor’s office, hospital, or special PFT lab.

Spirometry is especially helpful in diagnosing asthma and COPD. This is because it tests how much air you can exhale from your lungs after taking in a big breath and how fast you can blow out all that air.

For this test, you’ll sit upright in front of a spirometry machine attached to a plastic mouthpiece. It’s important that the mouthpiece fits snugly so that all the air you breathe goes into the machine. You’ll also wear a nose clip to keep you from breathing air out through your nose.

The respiratory technologist will explain how to breathe for the test. They’ll ask you to take a deep breath in, then exhale as forcefully and as quickly as you can until you empty your lungs. You’ll then be allowed to breathe as usual before repeating the test two more times.

You may also be asked to breathe in a medication that opens your airways. You’ll then take another deep breath and exhale into the machine again to see if the medication improved your lung function.

Cardiopulmonary exercise test

A cardiopulmonary exercise test (CPET) is a specialized exercise stress test to gauge your ability to exercise and to diagnose what may be restricting your activity levels. It’s usually performed on a treadmill or stationary bicycle in a doctor’s office or PFT lab.

CPET evaluates how the following perform during physical exertion:

  • your lungs
  • your heart
  • your blood vessels
  • your muscles

CPET also measures how much oxygen your body can use during exercise. Before the test, a nurse or technician will place monitors on your body including:

  • EKG leads to measure your heart rate
  • a blood pressure cuff
  • a pulse oximeter to measure oxygen saturation in the blood
  • a mouthpiece attached with a tube to a flow meter to measure how deeply and quickly you breathe and how much oxygen and carbon dioxide flow in and out of your lungs

The test itself lasts about 10 to 12 minutes. You begin by walking or pedaling slowly for a few minutes. After that, the treadmill will move faster or the resistance will increase on the stationary bicycle until you need to stop. Before stopping entirely, however, you will continue walking or pedaling at a slow rate to cool down.

Bronchial provocation test

A bronchial provocation test evaluates the sensitivity of your lungs. It’s often used to diagnose or rule out asthma as a cause of your symptoms.

The test can take one of three forms:

  • Irritant challenge. Your doctor exposes you to an asthma trigger, such as smoke or a chemical to see if your airways react.
  • Exercise challenge. You exercise on a treadmill or stationary bicycle to see if physical exertion makes the airways react.
  • Methacholine challenge. You inhale increasing doses of the chemical metacholine, which causes the airways to constrict with low doses among people with asthma and with high doses in people without asthma. If there is no reaction at low doses, your doctor will look for another cause of your symptoms.

Exhaled nitric oxide test

Like spirometry, an exhaled nitric oxide test requires you to breathe in deeply and then exhale fully into a mouthpiece attached to a monitor that measures the amount of nitric oxide in your breath.

An elevated level of nitric oxide in your breath suggests inflammation in your airways and possibly allergic asthma. The appropriate treatment is usually corticosteroids to reduce the inflammation.

Pulse oximetry test

Unlike most other PFTs, a pulse oximetry test does not require breathing into a machine or monitored exercising. The purpose of this test to measure the saturation of oxygen in your red blood cells.

It’s a noninvasive test, in which a pulse oximeter is placed on a finger usually, but it may also be placed on the forehead or a toe or other part of the body.

Results can be obtained almost instantaneously. If it appears that your oxygen levels are typical — around 95 percent — that’s one sign of healthy lung function.

However, if oxygen levels are below this level, it can be a sign of COPD, asthma, pneumonia, or other respiratory condition. It may also suggest that you need supplemental oxygen — at least temporarily — to maintain healthy organ function.

Plethysmography test

A plethysmography test measures the volume of gas in your lungs, known as lung volume. For this test, you’ll sit or stand in a small booth and breathe into a mouthpiece. Your doctor can learn about your lung volume by measuring the pressure in the booth.

Diffusion capacity test

This test evaluates how well the small air sacks inside the lungs, called alveoli, work. For this part of a pulmonary function test, you will be asked to breathe in carbon monoxide.

You may also breathe in a “tracer gas” for one breath. The machine can detect when you breathe out this gas. This tests how well your lungs are able to transfer oxygen and carbon dioxide to and from your bloodstream.

Because PFTs are trying to assess the true nature of your lung function, you may need to take certain steps prior to the test. For example, you may need to stop taking medications for asthma or chronic bronchitis that open your airways.

Your doctor should explain any changes to your medication routine ahead of time. You may have to avoid taking medications for pain, both prescription and over-the-counter drugs, because they may interfere with test results.

If you have questions, be sure to call your doctor’s office before the day of the test.

What to avoid on the day of your test

You should also avoid the following on the day of your test:

  • eating a large meal
  • consuming coffee, tea, chocolate, or other items containing caffeine
  • smoking at least 1 hour before the test
  • strenuous exercise

Other considerations

Be sure to wear loose clothing to the test, particularly if you will be walking on a treadmill or riding a stationary bike. Tighter clothing may restrict your breathing, even if you’re just sitting during the test.

Other considerations include:

  • Avoid wearing jewelry that might affect your breathing.
  • Wear dentures or other removable dental appliances to ensure your mouth will fit tightly around a mouthpiece used for the test.
  • Be prepared to rest after a test that requires exercise or multiple exhalations, as these can make you lightheaded or winded.
  • You may need to delay the test if you’ve recently had eye, chest, or abdominal surgery or a heart attack.

Some PFT results are available right away, especially if your doctor is present for the tests. In other cases, when a technician is administering the test, the results are then interpreted by a pulmonologist.

A pulmonologist is a doctor who specializes in lung health. They’ll review and interpret your tests and send the results to your doctor.

You may have to wait 48 to 72 hours to get those results and discuss them with your doctor.

A PFT can cause problems if you’ve:

  • recently had a heart attack
  • recently had eye surgery
  • recently had chest surgery
  • recently had abdominal surgery
  • have a severe respiratory infection
  • have unstable heart disease

PFTs are usually safe for most people. However, because the test may require you to breathe in and out quickly, you may feel dizzy or experience shortness of breath.

There’s also a risk that you may faint. If you feel lightheaded, tell your doctor. You may also want to arrange for someone to help you get home after the test.

If you have asthma, the test may cause you to have an asthma attack. In very rare cases, PFTs may cause a collapsed lung. If there are complications after the test, there will be medical professionals standing by to help.

PFTs are usually ordered if you’re having symptoms such as shortness of breath, wheezing, or coughing. They can be useful in diagnosing or ruling out certain respiratory conditions, but they are only some of the tools doctors use in making an accurate diagnosis and devising a treatment plan.

Most PFTs are short, simple tests of your breathing ability, though some involve exercise. If your doctor orders a PFT, be sure to find out how to prepare for that particular test. You may, for example, be advised against exercising or consuming caffeine the day of a test.