| Default Silo Topic 24479 Recycle Bin Oxygen Saturation Test Oxygen Saturation Test htmTPoxygen Oxygen Saturation Test 305312 InteliHealth 2000-12-06 f Harvard Medical School 2002-07-06
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Diagnostic Tests — Oxygen Saturation Test Oxygen Saturation Test What is the test? Your red blood cells must carry sufficient oxygen through your arteries to all of your internal organs in order for you to survive. Normally, when red blood cells pass through the lungs,95-100% of them are loaded or "saturated" with oxygen to carry. If you have lung disease or other types of medical conditions, fewer of your red blood cells will be carrying their usual load of oxygen and your oxygen "saturation" will be lower than 95%. Your blood oxygen level can be measured in two ways. What happens when the test is performed? An estimate of your oxygen saturation can be measured easily and painlessly with a clip that fits on your finger. This clip has a light that it shines through one side of your finger and a detector that measures the light that comes through the other side. The reason that this machine can make a good guess about your oxygen saturation is because blood cells are a bright red when they are loaded with oxygen and they change to a bluish color when they are no longer carrying a full load of oxygen. (This is why arteries are red and veins are blue in color.) Light that this machine shines through your finger is absorbed and reflected differently by red-colored cells passing through your finger compared with blue cells. This machine can not give a perfect estimate of your oxygen saturation. It is affected by some things as simple as red nail polish on your finger. It is also only able to give a rough estimate. A better test for measuring your oxygen saturation is called an arterial blood gas. For this test, a small sample of blood must be drawn directly out of an artery. Most routine blood tests use blood that is drawn out of a vein, so this test is a little different. The artery that is sampled most often is the radial artery in your wrist, that you can feel when you take your pulse. In order to draw blood from this artery, your doctor or a technician will feel your pulse before inserting the needle. Some patients find that it hurts a little more to have an artery sampled compared with a vein, but the procedure takes only a few seconds. Your arterial blood can be directly tested for its oxygen level, and other tests (such as the level of carbon dioxide and the pH of the blood) can be done as well. What risks are there from the test? The risks of an arterial blood gas are very small. Even temporary injury to your artery is unlikely to cause a problem, because most patients pump blood to their hand through more than one artery. Your doctor may do a special part of the physical examination before drawing your blood to make sure that you still get good blood flow to your hand even when one wrist artery is blocked. To do this test, the doctor will press down first on both sides of your wrist, to block blood flow, until your hand becomes pale. Then he or she will lift off the pressure from one side to see if that is enough to let your hand turn pink again. Must I do anything special after the test is over? You will need to have pressure held over the artery for a few minutes after the blood is drawn, because arteries are more likely to bleed afterward. How long is it before the result of the test is known? The results of the arterial blood gas are processed very quickly and are available within 15 minutes in most laboratories. The finger clip estimate of oxygen saturation is instantaneous. ©2000 President & Fellows of Harvard College
From Harvard Medical School Family Health Guide by Harvard Medical School. Copyright © 1999 by President and Fellows of Harvard College. Reprinted by permission of Simon & Schuster, Inc.
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