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What Does The Blood Oxygen Level Indicate & What To Do If You Have Low Blood Oxygen Levels?

The levels of blood oxygen indicate the amount of oxygen that is circulating within the bloodstream. Most of the oxygen that is present in the body is carried by the red blood cells. The red blood cells collect oxygen from the lungs and then deliver it to all the other parts of the body. The body has strict control over the blood oxygen levels and maintaining the exact balance of oxygenated blood is critical for your health. While there is no need to monitor your blood oxygen level, sometimes your blood oxygen level can fall below normal. So how do you know if your blood oxygen level is normal or not? Let’s take a look.

What Does The Blood Oxygen Level Indicate?

What Does The Blood Oxygen Level Indicate?

The blood oxygen levels indicate the amount of oxygen that the red blood cells are carrying in the body. The body closely monitors the levels of blood oxygen. Controlling the balance of oxygen-saturated blood is very important for your health.

While most adults and children do not need to monitor the level of blood oxygen, in case if you experience signs such as chest pain or shortness of breath, then your doctor might check the same. Otherwise, most doctors do not bother checking your blood oxygen level.

People who have chronic health issues often need to have their blood oxygen levels monitored regularly. This includes people who suffer from heart disease, asthma and COPD (chronic obstructive pulmonary disease). In such cases, doctors recommend regular monitoring of your blood oxygen level to determine if the prescribed treatments are working or if they require changing or adjustments.

How is Blood Oxygen Level Measured?

Blood oxygen levels can be measured with two separate tests. These include:

Arterial Blood Gas (ABG) Test

Arterial blood gas (ABG) test is a simple blood test that measures the blood oxygen level and also detects the level of other gases that are present in your bloodstream. It is also able to detect the pH (acid/base level) in the blood. The results of an ABG test is believed to be highly accurate, but it is an invasive test.

In order to get an ABG measurement done, your doctor will need to draw blood from an artery, instead of a vein. This is why the test is said to be invasive because unlike taking blood from the veins, arteries have a pulse that can be felt. The blood is drawn from the arteries because that blood is oxygenated, whereas the blood in your veins is not oxygenated.

Usually, the artery present in your wrist is used since it can be easily felt as compared to the other arteries in your body.

The wrist is known to be a sensitive area, which makes it uncomfortable to have blood drawn from here, as compared to the vein present near your elbow.

Another fact that adds to your discomfort is that arteries are deeper than veins, so it takes a bit more time to draw the blood.

Pulse Oximeter Test

A pulse oximeter (commonly referred to only as pulse ox) is another way to measure blood oxygen levels. A pulse ox is a device (non-invasive) that helps estimate the level of oxygen present in your blood. It works by sending infrared light into your capillaries that are in your toe, fingers, or earlobe. After this, it measures how much of the light has been reflected off these gases.(1)

A reading from the pulse oximeter helps indicate what percentage of the blood is saturated. The test, however, has a two percent error margin. This means that the reading might be off by 2 percent – either higher or lower than what your actual blood oxygen level is. Most doctors also consider this test to be slightly less accurate than the ABG test, but usually, this test is more comfortable to perform, and it is also non-invasive. Due to this, doctors typically rely on a pulse oximeter test for getting a quick reading.

Keep in mind, though, that even things like wearing dark-colored nail polish or cold extremities might cause the test to read lower than your actual levels. Your doctor might also ask you to remove your nail polish before using the device or if you are getting abnormally low readings of blood oxygen.

Since this test is non-invasive, you can even perform it yourself. You just need to purchase a pulse ox machine that is available easily at most chemist shops or even online. You should, however, consult your doctor first before using a home device in order to understand how to best interpret the results.

What Should Be The Normal Blood Oxygen Level?

The measurement of your blood oxygen is referred to as the oxygen saturation level. You might also hear it being called as O2 sat or PaO2 on a blood gas in medical terminology, especially while using a pulse ox machine. These guidelines serve as an indication of what your blood oxygen level test results might mean:

Normal Levels: A normal ABG measure for blood oxygen level for healthy lungs should range between 80 to 100 millimeters of mercury or mm Hg. If a pulse oximeter machine is being used for measuring your blood oxygen level, then a normal reading is usually taken to be between 95 and 100 percent.

However, if you have COPD or some other lung disease, then these normal ranges do not apply to your condition. Your doctor will then let you know what levels to expect from the reading as per your condition. For example, in people with severe COPD, it is not uncommon to witness a pulse ox level between 88 to 92 percent.(2)

Below Normal: Having a below-normal level of blood oxygen is known as hypoxemia. Hypoxemia is generally a cause of concern, and the lower is your blood oxygen level, the more severe is the hypoxemia. This can cause some other complications in your organs and body tissue.

Generally, a PaO2 reading that is below 80 mm Hg or having a pulse ox below 95 percent is considered to be a low reading. It is essential to know what is the normal reading for you, particularly if you have an underlying medical condition or a chronic lung disorder. Your doctor will provide you with the recommended ranges of oxygen levels that are acceptable to your individual health.

Above normal readings: If you are breathing unassisted, then it is generally difficult for the blood oxygen levels to become too high. In most cases, high levels of blood oxygen are known to occur in people who are using supplemental oxygen. This is usually detecting with the help of an ABG blood test.

What To Do If You Have Low Blood Oxygen Levels?

When the levels of blood oxygen go below the typical range, then you are likely to experience the following symptoms:

You might also start showing signs of cyanosis if you continue to have low blood oxygen levels for a longer period of time. The typical sign of cyanosis is the blue discoloration of your skin, mucous membranes, and nail beds.

The condition of cyanosis is considered to be a medical emergency, and if you are experiencing the symptoms of cyanosis, then you need to get immediate medical attention. Cyanosis can also cause respiratory failure, which is a life-threatening situation.

Low levels of blood oxygen can be caused by many conditions. These include:

These medical conditions are known to prevent your lungs from being able to adequately inhale oxygenated air and also exhaling carbon dioxide. Similarly, blood disorders or any condition with your circulatory system is also likely to prevent the blood from carrying oxygen properly throughout the body.

These medical conditions or any other disorders or health problems can also cause a decline in the oxygen saturation levels, and as the blood oxygen levels fall, you will start to experience the signs and symptoms of hypoxemia.

People are regular smokers are also known to have an inaccurate pulse ox reading. Smoking leads to the build-up of carbon monoxide in the blood and a pulse ox test is not able to differentiate between oxygen and this other type of gas present in the blood. If you are a smoker and you need to determine your blood oxygen level, then an ABG test is the better option for getting an accurate reading.

If you find that your blood oxygen level significantly below average, then you need to increase the oxygen saturation in the body. This is usually done by providing supplemental oxygen. However, home supplemental oxygen is considered to be a medication, and you can only get it on a doctor’s prescription. You also need to follow your doctor’s recommendations on how you should use home oxygen so as to avoid any complications. It is usually expensive to get home supplemental oxygen, and you can check with your insurance on whether the expense is covered.


There is no need for most people to regularly monitor the levels of blood oxygen. Only people who have health issues that are known to cause low blood oxygen levels need to have their blood oxygen levels monitored regularly. In such cases also, the less invasive technique of pulse oximetry is usually used more than the invasive test ABG.

Even though there is a margin of error involved with the pulse ox test readings, it is still accurate enough to be considered. If your doctor requires a more precise reading, then they will order the ABG blood test.


  1. Tremper, K.K., 1989. Pulse oximetry. Chest, 95(4), pp.713-715.
  2. Abdo, W.F., and Heunks, L.M., 2012. Oxygen-induced hypercapnia in COPD: myths and facts. Critical Care, 16(5), p.323
Sheetal DeCaria, M.D.
Sheetal DeCaria, M.D.
Written, Edited or Reviewed By: Sheetal DeCaria, M.D. This article does not provide medical advice. See disclaimer
Last Modified On:July 28, 2021

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