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What your blood oxygen level shows
Blood oxygen is a measure of how much oxygen red blood cells carry. Your body closely regulates the amount of oxygen in your blood. Maintaining a precise balance of oxygen saturation in your blood is vital to your health.
Most children and adults don’t need to monitor their blood oxygen level. In fact, many doctors won’t check it unless you’re showing signs of a problem, like shortness of breath or chest pain.
However, people with chronic health conditions many need to monitor their blood oxygen level. This includes asthma, heart disease, and chronic obstructive pulmonary disease (COPD).
In these cases, monitoring your blood oxygen level can help determine if treatments are working, or if they should be adjusted.
How your blood oxygen level is measured
Your blood oxygen level can be measured with two different tests:
Arterial blood gas
An arterial blood gas (ABG) test is a blood test. It measures your blood’s oxygen level. It also can detect the level of other gases in your blood, as well as the pH (acid/base level). An ABG is very accurate, but it’s invasive.
To get an ABG measurement, your doctor will draw blood from an artery rather than a vein. Unlike veins, arteries have a pulse that can be felt. Also, blood drawn from arteries is oxygenated. Blood in your veins isn’t.
The artery in your wrist is used because it’s easily felt compared to others in your body.
The wrist is a sensitive area, making a blood draw there more uncomfortable compared to a vein near your elbow. Arteries are also deeper than veins, adding to the discomfort.
Pulse oximeter
A pulse oximeter (pulse ox) is a noninvasive device that estimates the amount of oxygen in your blood. It does so by sending infrared light into capillaries in your finger, toe, or earlobe. Then it measures how much light is reflected off the gases.
A reading indicates what percentage of your blood is saturated, known as the SpO2 level. This test has a 2 percent error window. That means the reading may be as much as 2 percent higher or lower than your actual blood oxygen level.
This test may be slightly less accurate, but it’s very easy for doctors to perform. So doctors rely on it for fast readings.
Because a pulse ox is noninvasive, you can perform this test yourself. You can purchase pulse ox devices at most stores that carry health-related products or online.
