Lung Function Blood Tests

Reviewed by: HU Medical Review Board

If you have chronic obstructive pulmonary disease (COPD), at some point your doctor will typically use tests to diagnose or understand disease progression. One category of these tests is called lung function blood tests.1

What are lung function blood tests?

Lung function blood tests work by directly measuring the levels of certain gasses in the blood. This can provide information on how well the lungs are working.1

Our lungs have 2 important jobs related to gasses in our body. First, our lungs absorb oxygen from the air we breathe and move it into our blood. Our lungs also remove carbon dioxide, which is a waste product, from the bloodstream. We then breathe out this carbon dioxide.2

If someone’s lungs are not working properly, there can be too much carbon dioxide in the blood, or not enough oxygen. Both scenarios can cause serious health problems.2

People with COPD have lung damage that keeps the transfer of oxygen and carbon dioxide from working as well as it should. Lung function blood tests are used to show if a person has this kind of lung damage, and if so, how much damage there is. The tests work by measuring the amount of oxygen and carbon dioxide in a person’s blood.1,2

There are 2 main types of blood tests for people who have or doctors suspect they have COPD:1

  • Pulse oximetry test
  • Arterial blood gas test

There are also special kinds of exercise tests that monitor a person’s blood before, during, and after exercise. They can also be used to show how much oxygen someone might need while exercising and while at rest.1

Pulse oximetry

A pulse oximetry is a simple and straightforward test to measure the amount of oxygen in your blood. It is performed using a small device called a pulse oximeter. The pulse oximeter clips onto your finger, toe, ear, or foot. It works by shining a light through your skin and analyzing the light after it passes through you. It can use these results to measure the amount of oxygen in your blood.3

A pulse oximetry test gives you a result called oxygen saturation. This is a measure of the amount of oxygen in your blood. A healthy number for oxygen saturation is usually higher than 90 percent. A very low result could be a sign that someone needs supplemental oxygen.3

Pulse oximetry tests are painless and easy. But they can sometimes give inaccurate results for people with long or fake nails, darker skin color, poor circulation, or thick skin. Because of this, pulse oximetry results alone do not give the entire picture of your lung health.3

Arterial blood gas tests

An arterial blood gas test measures the levels of both oxygen and carbon dioxide in a person’s blood. Instead of estimating it through the skin, during this test a blood sample is taken. This sample is sent to a lab where the levels of oxygen and carbon dioxide can be measured.4

This test uses blood taken from an artery, usually in the wrist. Arteries carry blood from the lungs and heart to the rest of the body, so blood from an artery should be rich in oxygen. This test measures the gas levels in blood before it has been sent to the rest of the body, where the oxygen is used up and carbon dioxide is produced.4

People with COPD may have lower levels of oxygen in the blood leaving the lungs. They may also have more carbon dioxide even in the fresh blood because the lungs were not able to effectively remove it. An arterial blood gas test is more exact than pulse oximetry, and it also measures carbon dioxide.4

Exercise tests

Exercise tests also work by measuring the levels of gas in someone’s blood. But the test is done during exercise. Two common types of exercise tests for people with COPD are:5

  • Exercise tolerance test – This test measures the levels of oxygen and carbon dioxide in a person’s blood before, during, and after exercising
  • Exercise for desaturation test – This test measures how much oxygen a person’s body requires while exercising versus resting

During the tests you will be asked to exercise using a treadmill or stationary bike. The test provider will use a pulse oximeter or an arterial blood gas test to measure your blood during or after this exercise. This provides information on how your lungs work during exercise. This can help doctors better understand how COPD impacts you.5

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