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Blood gases

BMJ Group Medical Reference

Usually, doctors test blood gases only if they think you have severe chronic obstructive pulmonary disease (COPD). Your doctor may think you have this because of your symptoms or because of the results of a spirometry test.

For this test a small amount of blood will be taken from an artery. It's important to get the blood from an artery (and not a vein) because the blood in arteries has the most oxygen. The test measures the oxygen and carbon dioxide in the blood sample.

The results tell the doctor:

  • Whether enough oxygen is getting into your blood from the air you breathe into your lungs

  • Whether enough carbon dioxide is getting out of your body after travelling through your bloodstream and into your lungs.

If you have severe COPD, your lungs are probably badly damaged. Because of this, your blood may not be able to absorb enough oxygen from them. With low levels of oxygen in your blood, you may feel out of breath and tired a lot, and many parts of your body may not be able to work properly.



Arteries are the blood vessels that take blood that is rich in oxygen and food away from your heart. The arteries carry this blood to all the tissues in your body.


Veins are blood vessels that carry blood back to your heart after your blood has delivered oxygen and food to the tissues.

For more terms related to Chronic obstructive pulmonary disease


For references related to Chronic obstructive pulmonary disease click here.
Last Updated: March 13, 2013
This information does not replace medical advice.  If you are concerned you might have a medical problem please ask your Boots pharmacy team in your local Boots store, or see your doctor.

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