What is a PFT (Pulmonary Function Test)?

What is a PFT (Pulmonary Function Test)?

A pulmonary function test (PFT) measures how well a pair of lungs work. These simple, low-risk tests can assist in diagnosis and treatment of lung disorders.

A physician may order a PFT to gain insight into a lung-related problem. They are common when diagnosing and monitoring chronic lung conditions, allergies, restrictive airway problems and respiratory infections. The test can also be used for patients with diseases like sarcoidosis and scleroderma.

Types of Pulmonary Function Tests


The most basic type of lung function test is spirometry, most often used to diagnose diseases like COPD and asthma. It measures rate of air flow and the volume of air the lungs can hold.

This test requires that a person breathes into a tube connected to a computer. Some breaths will be normal, but the test also requires breathing at maximal effort.

Lung Volume Test

A lung volume test is another way to measure how much air lungs can hold. It is more precise than spirometry because in addition to measuring the amount of air in the lungs, it also it measures the air remaining at the end of a normal breath.

This test is very similar to spirometry, but the person will perform the test in a small room with clear walls.

Lung Diffusion Capacity

A lung diffusion capacity test only requires normal breathing, so the risk of lightheadedness is very low. During the test, a person breathes in and out of a tube. The test itself only takes a few minutes, but the doctor may also require a blood sample to measure hemoglobin levels.

Arterial Blood Gas Test

Your lungs are responsible for taking oxygen from the air you breathe and transporting it throughout the body. If your healthcare professional is concerned about the levels of oxygen and carbon dioxide in your blood, they may recommend an arterial blood gas test. For this test, blood is taken from an artery in the wrist, then analyzed.

Fractional Exhaled Nitric Oxide Test (FeNO)

Nitric oxide is a marker for inflammation in the lungs. Fractional exhaled nitric oxide tests measure the amount of nitric oxide exhaled. A person simply exhales into a tube that is connected to a portable device.

Risks of PFTs

Pulmonary function testing has very little risk. Aside from tests that are accompanied by blood work, they are completely non-invasive. The most common issues include dizziness during the test, coughing, shortness of breath, or an asthma attack triggered by deep breathing.

If you have specific questions about any of these PFTs, don’t hesitate to ask your provider.

© 2020 Penn State Health