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.

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