Accessible Search Form           Advanced Search


National Heart Lung and Blood Institute Logo

For more information, visit http://www.nhlbi.nih.gov/health/health-topics/topics/lft/


What Are Lung Function Tests?

Lung function tests, also called pulmonary (PULL-mun-ary) function tests, measure how well your lungs work. These tests are used to look for the cause of breathing problems, such as shortness of breath.

Lung function tests measure:

  • How much air you can take into your lungs. This amount is compared with that of other people your age, height, and sex. This allows your doctor to see whether you're in the normal range.
  • How much air you can blow out of your lungs and how fast you can do it.
  • How well your lungs deliver oxygen to your blood.
  • The strength of your breathing muscles.

Doctors use lung function tests to help diagnose conditions such as asthma, pulmonary fibrosis (scarring of the lung tissue), and COPD (chronic obstructive pulmonary disease).

Lung function tests also are used to check the extent of damage caused by conditions such as pulmonary fibrosis and sarcoidosis (sar-koy-DOE-sis). Also, these tests might be used to check how well treatments, such as asthma medicines, are working.

Overview

Lung function tests include breathing tests and tests that measure the oxygen level in your blood. The breathing tests most often used are:

  • Spirometry (spi-ROM-eh-tre). This test measures how much air you can breathe in and out. It also measures how fast you can blow air out.
  • Body plethysmography (pleth-iz-MOG-ra-fe). This test measures how much air is present in your lungs when you take a deep breath. It also measures how much air remains in your lungs after you breathe out fully.
  • Lung diffusion capacity. This test measures how well oxygen passes from your lungs to your bloodstream.

These tests may not show what's causing breathing problems. So, you may have other tests as well, such as an exercise stress test. This test measures how well your lungs and heart work while you exercise on a treadmill or bicycle.

Two tests that measure the oxygen level in your blood are pulse oximetry and arterial blood gas tests. These tests also are called blood oxygen tests.

Pulse oximetry measures your blood oxygen level using a special light. For an arterial blood gas test, your doctor takes a sample of your blood, usually from an artery in your wrist. The sample is sent to a laboratory, where its oxygen level is measured.

Outlook

Lung function tests usually are painless and rarely cause side effects. You may feel some discomfort during an arterial blood gas test when the blood sample is taken.

For more information about healthy lung function, go to the Health Topics How the Lungs Work article.




Types of Lung Function Tests

Breathing Tests

Spirometry

Spirometry measures how much air you breathe in and out and how fast you blow it out. This is measured two ways: peak expiratory flow rate (PEFR) and forced expiratory volume in 1 second (FEV1).

PEFR is the fastest rate at which you can blow air out of your lungs. FEV1 refers to the amount of air you can blow out in 1 second.

During the test, a technician will ask you to take a deep breath in. Then, you'll blow as hard as you can into a tube connected to a small machine. The machine is called a spirometer.

Spirometry

The image shows how spirometry is done. The patient takes a deep breath and blows as hard as possible into a tube connected to a spirometer. The spirometer measures the amount of air breathed out. It also measures how fast the air was blown out.

The image shows how spirometry is done. The patient takes a deep breath and blows as hard as possible into a tube connected to a spirometer. The spirometer measures the amount of air breathed out. It also measures how fast the air was blown out.

Your doctor may have you inhale a medicine that helps open your airways. He or she will want to see whether the medicine changes or improves the test results.

Spirometry helps check for conditions that affect how much air you can breathe in, such as pulmonary fibrosis (scarring of the lung tissue). The test also helps detect diseases that affect how fast you can breathe air out, like asthma and COPD (chronic obstructive pulmonary disease).

Lung Volume Measurement

Body plethysmography (pleth-iz-MOG-re-fe) is a test that measures how much air is present in your lungs when you take a deep breath. It also measures how much air remains in your lungs after you breathe out fully.

During the test, you sit inside a glass booth and breathe into a tube that's attached to a computer.

For other lung function tests, you might breathe in nitrogen or helium gas and then blow it out. The gas you breathe out is measured to show how much air your lungs can hold.

Lung volume measurement can help diagnose pulmonary fibrosis or a stiff or weak chest wall.

Lung Diffusion Capacity

This test measures how well oxygen passes from your lungs to your bloodstream. During this test, you breathe in a type of gas through a tube. You hold your breath for a brief moment and then blow out the gas.

Abnormal test results may suggest loss of lung tissue, emphysema (a type of COPD), very bad scarring of the lung tissue, or problems with blood flow through the body's arteries.

Tests To Measure Oxygen Level

Pulse oximetry and arterial blood gas tests show how much oxygen is in your blood. During pulse oximetry, a small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood. This test is painless and no needles are used.

For an arterial blood gas test, a blood sample is taken from an artery, usually in your wrist. The sample is sent to a laboratory, where its oxygen level is measured. You may feel some discomfort during an arterial blood gas test because a needle is used to take the blood sample.

Testing in Infants and Young Children

Spirometry and other measures of lung function usually can be done for children older than 6 years, if they can follow directions well. Spirometry might be tried in children as young as 5 years. However, technicians who have special training with young children may need to do the testing.

Instead of spirometry, a growing number of medical centers measure respiratory system resistance. This is another way to test lung function in young children.

The child wears nose clips and has his or her cheeks supported with an adult's hands. The child breathes in and out quietly on a mouthpiece, while the technician measures changes in pressure at the mouth. During these lung function tests, parents can help comfort their children and encourage them to cooperate.

Very young children (younger than 2 years) may need an infant lung function test. This requires special equipment and medical staff. This type of test is available only at a few medical centers.

The doctor gives the child medicine to help him or her sleep through the test. A technician places a mask over the child's nose and mouth and a vest around the child's chest.

The mask and vest are attached to a lung function machine. The machine gently pushes air into the child's lungs through the mask. As the child exhales, the vest slightly squeezes his or her chest. This helps push more air out of the lungs. The exhaled air is then measured.

In children younger than 5 years, doctors likely will use signs and symptoms, medical history, and a physical exam to diagnose lung problems.

Doctors can use pulse oximetry and arterial blood gas tests for children of all ages.




Other Names for Lung Function Tests

  • Lung diffusion testing; also called diffusing capacity and diffusing capacity of the lung for carbon monoxide, or DLCO
  • Pulmonary function tests, or PFTs

Arterial blood gas tests also are called blood gas analyses or ABGs.




Who Needs Lung Function Tests?

People who have breathing problems, such as shortness of breath, may need lung function tests. These tests help find the cause of breathing problems.

Doctors use lung function tests to help diagnose conditions such as asthma, pulmonary fibrosis (scarring of the lung tissue), and COPD (chronic obstructive pulmonary disease).

Lung function tests also are used to check the extent of damage caused by conditions such as pulmonary fibrosis and sarcoidosis. Also, these tests might be used to check how well treatments, such as asthma medicines, are working.

Diagnosing Lung Conditions

Your doctor will diagnose a lung condition based on your medical and family histories, a physical exam, and test results.

Medical and Family Histories

Your doctor will ask you questions, such as:

  • Do you ever feel like you can't get enough air?
  • Does your chest feel tight sometimes?
  • Do you have periods of coughing or wheezing (a whistling sound when you breathe)?
  • Do you ever have chest pain?
  • Can you walk or run as fast as other people your age?

Your doctor also will ask whether you or anyone in your family has ever:

  • Had asthma or allergies
  • Had heart disease
  • Smoked
  • Traveled to places where they may have been exposed to tuberculosis
  • Had a job that exposed them to dust, fumes, or particles (like asbestos)

Physical Exam

Your doctor will check your heart rate, breathing rate, and blood pressure. He or she also will listen to your heart and lungs with a stethoscope and feel your abdomen and limbs.

Your doctor will look for signs of heart or lung disease, or another disease that might be causing your symptoms.

Lung and Heart Tests

Based on your medical history and physical exam, your doctor will recommend tests. A chest x ray usually is the first test done to find the cause of a breathing problem. This test takes pictures of the organs and structures inside your chest.

Your doctor may do lung function tests to find out even more about how well your lungs work.

Your doctor also may do tests to check your heart, such as an EKG (electrocardiogram) or an exercise stress test. An EKG detects and records your heart's electrical activity. A stress test shows how well your heart works during physical activity.




What To Expect Before Lung Function Tests

If you take breathing medicines, your doctor may ask you to stop them for a short time before spirometry, lung volume measurement, or lung diffusion capacity tests.

No special preparation is needed before pulse oximetry and arterial blood gas tests. If you're getting oxygen therapy, your doctor may ask you to stop using it for a short time before the tests. This allows your doctor to check your blood oxygen level without the added oxygen.




What To Expect During Lung Function Tests

Breathing Tests

Spirometry might be done in your doctor's office or in a special lung function laboratory (lab). Lung volume measurement and lung diffusion capacity tests are done in a special lab or clinic. For these tests, you sit in a chair next to a machine that measures your breathing. For spirometry, you sit or stand next to the machine.

Before the tests, a technician places soft clips on your nose. This allows you to breathe only through a tube that's attached to the testing machine. The technician will tell you how to breathe into the tube. For example, you might be asked to breathe normally, slowly, or rapidly.

Some tests require deep breathing, which might make you feel short of breath, dizzy, or light-headed, or it might make you cough.

Spirometry

For this test, you take a deep breath and then exhale as fast and as hard as you can into the tube. With spirometry, your doctor may give you medicine to help open your airways. Your doctor will want to see whether the medicine changes or improves the test results.

Lung Volume Measurement

For body plethysmography, you sit in a clear glass booth and breathe through the tube attached to the testing machine. The changes in pressure inside the booth are measured to show how much air you can breathe into your lungs.

For other tests, you breathe in nitrogen or helium gas and then exhale. The gas that you breathe out is measured.

Lung Diffusion Capacity

During this test, you breathe in gas through the tube, hold your breath for 10 seconds, and then rapidly blow it out. The gas contains a small amount of carbon monoxide, which won't harm you.

Tests To Measure Oxygen Level

Pulse oximetry is done in a doctor's office or hospital. An arterial blood gas test is done in a lab or hospital.

Pulse Oximetry

For this test, a small sensor is attached to your finger or ear using a clip or flexible tape. The sensor is then attached to a cable that leads to a small machine called an oximeter. The oximeter shows the amount of oxygen in your blood. This test is painless and no needles are used.

Arterial Blood Gas

During this test, your doctor or technician inserts a needle into an artery, usually in your wrist, and takes a sample of blood. You may feel some discomfort when the needle is inserted. The sample is then sent to a lab where its oxygen level is measured.

After the needle is removed, you may feel mild pressure or throbbing at the needle site. Applying pressure to the area for 5 to 10 minutes should stop the bleeding. You'll be given a small bandage to place on the area.




What To Expect After Lung Function Tests

You can return to your normal activities and restart your medicines after lung function tests. Talk with your doctor about when you'll get the test results.




What Do Lung Function Tests Show?

Breathing Tests

Spirometry

Spirometry can show whether you have:

  • A blockage (obstruction) in your airways. This may be a sign of asthma, COPD (chronic obstructive pulmonary disease), or another obstructive lung disorder.
  • Smaller than normal lungs (restriction). This may be a sign of heart failure, pulmonary fibrosis (scarring of the lung tissue), or another restrictive lung disorder.

Lung Volume Measurement

These tests measure how much air your lungs can hold when you breathe in and how much air is left in your lungs when you breathe out. Abnormal test results may show that you have pulmonary fibrosis or a stiff or weak chest wall.

Lung Diffusion Capacity

This test can show a problem with oxygen moving from your lungs into your bloodstream. This might be a sign of loss of lung tissue, emphysema (a type of COPD), or problems with blood flow through the body's arteries.

Tests To Measure Oxygen Level

Pulse oximetry and arterial blood gas tests measure the oxygen level in your blood. These tests show how well your lungs are taking in oxygen and moving it into the bloodstream. A low level of oxygen in the blood might be a sign of a lung or heart disorder.




What Are the Risks of Lung Function Tests?

Spirometry, lung volume measurement tests, and lung diffusion capacity tests usually are safe. These tests rarely cause problems.

Pulse oximetry has no risks. Side effects from arterial blood gas tests are rare.




Links to Other Information About Lung Function Tests

NHLBI Resources

Non-NHLBI Resources

Clinical Trials

 
September 17, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.