Medical Content Created by the Faculty of the
Harvard Medical School
Your red blood cells carry oxygen through your arteries to all of your internal organs. They must carry enough oxygen to keep you alive. Normally, when red blood cells pass through the lungs, 95%-100% of them are loaded, or "saturated," with oxygen. If you have lung disease or other types of medical conditions, fewer of your red blood cells may be carrying their usual load of oxygen, and your oxygen saturation might be lower than 95%. If your blood oxygen saturation is too low, you may need to be given oxygen to breathe.