First Time User? Enroll now.
COVID-19: Vaccine information and additional resources | Medicaid: The program is changing and you must take steps to keep your UNC Health providers
Home > Health Library > Lung Function Tests
Lung function tests check to see how well your lungs work. The tests can find lung problems, measure how serious they are, and check to see how well treatment for a lung disease is working.
The tests look at:
Types of lung function tests include:
You may also hear the tests called pulmonary function tests, or PFTs.
Lung function results are measured directly in some tests and are calculated in others.
No single test can check for all of the lung function values, so more than one type of test may be done. Some tests may be repeated after you inhale medicine that enlarges your airways (bronchodilator).
There are several different types of lung function tests.
Spirometry is the most common lung function test. It measures how much and how quickly you can move air out of your lungs. You breathe into a mouthpiece attached to a machine called a spirometer. The machine records your results.
This test can measure many different things about the way you breathe. These include how much air you can exhale, how much air you can breathe in and out in 1 minute, and the amount of air left in your lungs after a normal exhale.
Gas diffusion tests measure the amount of oxygen and other gases that move through the lungs' air sacs (alveoli) per minute. These tests let you know how well gases are being absorbed into your blood from your lungs. Gas diffusion tests include:
Body plethysmography may be used to measure:
Inhalation challenge tests are done to measure how your airways respond to substances that may be causing asthma or wheezing. These tests are also called provocation studies.
During the test, you inhale increasing amounts of a substance through a nebulizer. This is a device that uses a face mask or a mouthpiece to deliver the substance in a fine mist (aerosol). Spirometry readings are taken to look at lung function before, during, and after you inhale the substance.
Exercise stress tests look at how exercise affects your lungs. Spirometry readings are done after exercise and then again at rest.
The multiple-breath washout test is done to check people who have cystic fibrosis. For this test, you breathe through a tube. First you breathe air that contains a tracer gas. Then you breathe regular air while the amount of tracer gas you exhale is monitored. Test results are reported as a lung clearance index (LCI). A high LCI value means that the lungs aren't working well.
Lung function tests are done to:
Lung function tests are usually done in special rooms that have all of the right equipment.
For most of the tests, you'll wear a nose clip to keep air from leaking through your nose. Then you'll breathe into a mouthpiece connected to a recording device.
The exact steps depend on which test you have. For example, you may be asked to inhale as deeply as you can and then to exhale as fast and as hard as you can. You also may be asked to breathe in and out as deeply and as fast as you can for 15 seconds.
Some tests may be repeated after you have inhaled a spray containing medicine that expands the airways in your lungs. You may be asked to breathe a special mixture of gases, such as 100% oxygen, a mixture of helium and air, or a mixture of carbon monoxide and air.
Sometimes a sample of blood may be taken from an artery in your wrist to measure blood gases.
If you have body plethysmography, you will be asked to sit inside a small enclosure. It's like a phone booth, with windows that allow you to see out. The booth measures small changes in pressure that occur as you breathe.
The accuracy of the tests depends on how well you can follow all of the instructions. The therapist may ask you to breathe deeply during some of the tests to get the best results.
The testing may take from 5 to 30 minutes, depending on how many tests you have.
If you have an arterial blood gas test, you may feel some pain from the needle used to collect the blood. The other lung function tests are usually painless. Some of the tests may be tiring for people who have a lung disease.
You may cough or feel lightheaded after breathing in or out rapidly, but you will be given a chance to rest between tests. It may not be comfortable to wear the nose clip or to breathe through the mouthpiece.
If you have body plethysmography, you may feel uncomfortable in the airtight booth. But the therapist will be nearby to open the door if you feel too uncomfortable.
If you are given breathing medicine, it may cause you to shake or may increase your heart rate. If you feel any chest pain or discomfort, tell the therapist right away.
For a healthy person, there's little or no risk in taking these tests. If you have a serious heart or lung condition, discuss your risks with your doctor.
Most test results are ready right away.
Results are in the normal range for a person with healthy lungs.
Test results are outside of the normal range for a person with healthy lungs. This may be a sign of some kind of lung disease. There are two main types of lung disease that can be found with lung function tests: obstructive and restrictive.
Obstructive lung conditions cause the airways to get narrower.
Examples include emphysema, bronchitis, asthma, and infection that produces inflammation.
Lung function test
What the test measures
Result as predicted for age, height, sex, weight, or race
Forced vital capacity (FVC)
How much air you can exhale with force after you inhale as deeply as you can.
Normal or lower than predicted value
Forced expiratory volume (FEV1)
How much air you can exhale with force in one breath.
FEV1 divided by FVC
See the first two tests above.
Forced expiratory flow 25% to 75%
How much air you can breathe out halfway through an exhale.
Peak expiratory flow (PEF)
How much air you can quickly exhale when you try your hardest.
Maximum voluntary ventilation (MVV)
The greatest amount of air you can breathe in and out during 1 minute.
Slow vital capacity (SVC)
How much air you can slowly exhale after you inhale as deeply as you can.
Normal or lower
Total lung capacity (TLC)
The amount of air in your lungs after you inhale as deeply as you can.
Normal or higher
Functional residual capacity (FRC)
The amount of air in your lungs at the end of a normal exhaled breath.
Residual volume (RV)
The amount of air in your lungs after you have exhaled completely.
Expiratory reserve volume (ERV)
The difference between the amount of air in your lungs after a normal exhale (FRC) and the amount after you exhale with force (RV).
RV divided by TLC ratio
See the test above.
Restrictive lung conditions cause a loss of lung tissue, a decrease in the lungs' ability to expand, or a decrease in how well the lungs can transfer oxygen or carbon dioxide in or out of the blood.
Examples include scleroderma, pulmonary fibrosis, and sarcoidosis. Other restrictive conditions include some chest injuries, being very overweight (obesity), pregnancy, and loss of lung tissue due to surgery.
Lower than predicted value
Normal, lower, or higher
Current as of:
July 6, 2021
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineAdam Husney MD - Family MedicineElizabeth T. Russo MD - Internal Medicine
Current as of: July 6, 2021
Author: Healthwise Staff
Medical Review:E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & Elizabeth T. Russo MD - Internal Medicine
To learn more about Healthwise, visit Healthwise.org.
© 1995-2021 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.