Pulmonary function tests (PFT) are a group of tests that determine how well the lungs work. This includes tests to assess how well you’re able to breathe and how effectively lungs are able to carry oxygen to the rest of the body.
Pulmonary Function Test

Why Are Pulmonary Function Tests Done?

The health care provider may ask you to do these tests if you’re continually exposed to toxic elements in the workplace, to monitor how effectively lungs are functioning post-surgery or treatment and to diagnose if you’re experiencing any symptoms associated with lung disorders like:



Chronic bronchitis

Chronic obstructive pulmonary disease (COPD)

Damaged lung tissue

Sarcoidosis, a collection of inflammatory cells around organs

Lung cancer


Enlarged airways


Muscle weakness in the wall of the chest

Proper diagnosis may help a person get the right treatment.

Also Read: World Asthma Day 2020: Learn About The Causes, Types, Symptoms, Diagnosis, Treatment And Prevention

What Happens During Pulmonary Function Tests?

The doctor may choose tests based on what condition they need to diagnose. Each test works entirely in a different way.


Spirometry is one of the most common pulmonary function tests, which measures how much air you can breathe in and out, while it also assesses how fast you can empty the air out of your lungs.

Spirometry helps to diagnose breathing issues like asthma and COPD. Moreover, this test can also help the doctor to determine if the medications for asthma is working or not.

During the test, the person should breathe in as much air as he can and then quickly blow out as much air via a tube connected to a machine called a spirometer.

This test measures two things:

The results will let the physician know if a person is able to breathe normally.

The amount of air exhaled in 1 second is measured and the score reveals the doctor about the severity of the breathing problem.

Body Plethysmography

In this test, the person has to breathe in deeply, which determines how much air is in the lungs while inhaling. It also monitors how much air stays in the lungs after the person breathes out to his maximum limit.

Plethysmography is done for several reasons including:

The physician may suggest doing this test to assess how a condition such as COPD or asthma affects the lungs. The test is painless and takes about 15 minutes to complete, during plethysmography the patient is made to sit in a clear plastic box wearing a nose clip and asked to breathe through the mouth via a special mouthpiece.

This test may also help the doctor change the treatment plan according to the severity of the problem.

It can also help physicians confirm whether a person has a lung problem that reduces the amount of space in the lungs and this condition is known as restrictive disease.

Furthermore, it shows if the airways are narrowed that may help the physician to decide whether lung medications such as bronchodilators could help. In addition, it may also help physicians find out if the patient needs any surgery.

Lung Diffusion Capacity

A lung diffusion capacity test evaluates how well oxygen moves from the lungs into the system. It is quite similar to spirometry. The person is made to breathe into a tube attached to a machine.

This test diagnose health condition of the blood vessels between the heart and lungs, and also show the extent of damage caused due to a disease such as emphysema.

Bronchial Provocation Test

For patients suffering from asthma certain triggers such as exercise, smoke and dust can abruptly make it difficult to breathe. A bronchial provocation test can help diagnose asthma and its severity.

During the test, the person inhales a medication that makes airways narrow, then a spirometry test is done and repeated several times. The physician will use the readings to assess how much airways narrow during an asthma attack.

Cardiopulmonary Exercise Stress Test

This test evaluates lung and heart health. It’s generally performed for people who may have heart or lung problems. Sometimes, these problems may show up only during exercise.

During the test, the person is made to walk on a treadmill. The doctor checks on heart rate, as the heart beats faster and faster. The person is asked to breathe into a tube that examines the lung function as they work harder.

Also Read: Pulse Oximeter: Benefits, Readings And How It Works

Pulse Oximetry Test

This is a painless and non-invasive test that measures the oxygen level in the blood. A clip is connected to the finger or earlobe or another part of the skin. The device uses light to assess the level of oxygen in the red blood cells.

Arterial Blood Gas Test

This test determines the levels of gases like oxygen and carbon dioxide in blood taken from arteries.

The technician will use a needle to take the blood sample from the wrist and then assess the sample for the levels of gases.

Fractional Exhaled Nitric Oxide Test

Patients suffering from certain kinds of asthma might have high levels of a gas called nitric oxide in the blood. This test measures how much nitric oxide is present in the air a person breathes out. During the test, the person should breathe out slowly and steadily into a tube that’s connected to a portable device.

How to Prepare for Pulmonary Function Tests?

The doctor will explain to the patient about the test and what to expect. Wear loose clothing and comfortable shoes when going for the tests. For the best results follow these steps:

  • Take all regular medications before the test, unless your doctor suggests not to.
  • Don’t smoke before the test and also ask your doctor how long before the test you should stop.
  • Patients using a short-acting inhaler should avoid using it 6-8 hours before the test.
  • Avoid drinking alcohol at least 4 hours before the test.
  • Refrain from having a meal at least 2 hours before the test.
  • Don’t do any hard physical activities at least 30 minutes before the test.

Pulmonary Function Test Results

Most pulmonary function tests take about 15-30 minutes. You can resume normal activities after 30 minutes. Certain things that can affect the accuracy of the results include:

How precisely the person follow the instructions

Medications that affect the airways

Pain killers


Stomach bloating


A result that’s abnormal indicates that a person has a lung disorder. The doctor will discuss  with the patient about the results and further treatment plan.