After you breathe in oxygen, it goes through your lungs and into your bloodstream. The amount of oxygen in your blood is your blood oxygen level. Your body needs a certain amount of oxygen in order to function properly, and low blood oxygen levels can lead to serious complications.
Your blood oxygen level (blood oxygen saturation) is the amount of oxygen you have circulating in your blood.
Oxygen is essential to life, and our bodies need a certain amount of oxygen to function properly. Oxygen enters your body through your nose or mouth when you breathe (inhale) and passes through your lungs into your bloodstream. Once in your bloodstream, the oxygen then goes to cells all over your body. All of your cells need oxygen to create energy efficiently, and your body needs energy to fulfill all of its processes, such as digestion and even thinking.
Once your cells use oxygen, they create carbon dioxide. Your bloodstream then carries the carbon dioxide back to your lungs, and you breathe it out (exhale it) through your mouth or nose.
Your body tightly regulates the amount of oxygen saturation in your blood, because low blood oxygen levels (hypoxemia) can lead to many serious conditions and damage to individual organ systems, especially your brain and heart. Low blood oxygen levels indicate that your lungs and/or circulatory system may not be working as they should.
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There are two main ways to measure or test blood oxygen levels: through a blood draw test and through pulse oximetry (using an oximeter). A blood draw test provides much more information about your oxygen levels than an oximeter does.
Healthcare providers can measure your blood oxygen level as part of a larger test known as an arterial blood gas (ABG) test. An ABG test measures the level of oxygen and carbon dioxide in your blood. The test also checks the balance of acids and bases, known as the pH balance, in your blood. Having too much or too little acid in your blood can be harmful to your health.
A pulse oximeter can also measure blood oxygen saturation levels through a small clip that’s usually placed on your finger or toe. An oximeter reading only indicates what percentage of your blood is saturated with oxygen, known as the SpO2 level, as well as your heart rate. It’s a quick and harmless way to check if someone’s blood oxygen level is too low.
Healthcare providers use pulse oximeters frequently in hospitals. You can also use a pulse oximeter at home — you can usually buy one from a pharmacy or certain stores and websites.
Your healthcare provider may have you undergo a blood oxygen level test if you’re experiencing any of the following acute (sudden and serious) conditions:
Your provider may also perform a blood oxygen test if you have any of the following lung conditions to make sure your treatment is working properly:
If you’re receiving oxygen therapy while in a hospital, your provider will likely monitor your blood oxygen level to make sure you are getting the right amount of oxygen.
There are some ways to naturally increase the amount of oxygen in your blood, including:
You can use a pulse oximeter at home to check your blood oxygen level and see if these natural ways to increase your oxygen intake work for you.
However, it’s important to note that if you have an underlying condition, especially a severe illness such as pneumonia or carbon monoxide poisoning, these natural remedies may not be enough to increase your blood oxygen to an acceptable level.
If you experience signs of hypoxemia, get to the nearest hospital as soon as possible.
A healthcare provider specialist called a respiratory therapist usually performs blood draws for blood oxygen level tests that are a part of arterial blood gas tests from an artery in your wrist. The sample is then either processed by the respiratory therapist or sent to a lab very quickly where medical laboratory scientists process the sample.
Any healthcare provider can apply a pulse oximeter to check your blood oxygen saturation level. You can also use a pulse oximeter on yourself or someone else at home.
If a respiratory therapist is taking a blood sample from an artery in your wrist, they may perform a blood circulation test called an Allen test before taking the sample. An Allen test involves holding your hand high with a clenched fist. Your provider will then apply pressure to the arteries in your wrist for several seconds. This simple test makes sure both of the arteries in your wrist are open and working properly.
If you’re on supplemental oxygen therapy, your provider may turn off your oxygen for about 20 minutes before the blood draw. This is called a room air test. If you’re unable to breathe without supplemental oxygen, your provider will not do this test.
Most blood tests take a blood sample from one of your veins. For a blood oxygen level test that’s part of an arterial blood gas test, a respiratory therapist will take a sample of blood from one of your arteries. This is because there are higher oxygen levels in blood from an artery than blood from a vein.
A respiratory therapist usually takes the sample from an artery inside your wrist known as the radial artery. Sometimes they may take a sample from an artery in your elbow or groin. If a newborn is undergoing a blood oxygen level test, they may take the sample from the baby's heel or umbilical cord.
Unfortunately, getting a blood sample from an artery is usually more painful than getting a sample from a vein. This is because arteries are deeper than veins and are surrounded by nerves. You may feel light-headed, dizzy or nauseated while a respiratory therapist takes blood from your artery.
A blood oxygen level test blood draw includes the following steps:
A blood oxygen saturation test with the use of a pulse oximeter includes the following steps:
You can also use a pulse oximeter at home. It’s important to keep in mind the factors that can reduce the accuracy of pulse oximeter readings, which include:
If you’ve had a blood draw, you may experience some bruising and/or soreness at the site of the needle injection. Your provider may recommend that you avoid lifting heavy objects for 24 hours after the blood draw.
Blood test reports, including blood oxygen level test reports, usually provide the following information:
If your blood oxygen level blood test results are not normal, it may mean you:
A blood oxygen level test can't diagnose specific conditions. If your results are not normal, your healthcare provider will have you undergo more tests to confirm or rule out a diagnosis.
Laboratories may have different reference ranges for the aspects of your blood that are measured in a blood oxygen level test. When you get your blood test results back, there will be information that indicates what that lab’s normal ranges are for each measurement. If you have any questions about your results, be sure to ask your healthcare provider.
For most people, a normal pulse oximeter reading for your oxygen saturation level is between 95% and 100%. If you have a lung disease such as COPD or pneumonia, your normal oxygen saturation level may be lower. Your healthcare provider will let you know what levels are acceptable. Your oxygen saturation levels may also be lower if you live in an area with high elevation.
It’s important to note that pulse oximeters are not always accurate. Your actual blood saturation level may be 2% to 4% higher or lower than what the oximeter reads. For a more accurate result, your provider may check your blood oxygen levels with a blood test.
A lower-than-normal blood oxygen level is called hypoxemia. Since oxygen is essential to all of your body’s functions, hypoxemia is often concerning. The lower the oxygen level, the greater likelihood for complications in body tissue and organs.
A variety of conditions and circumstances can interfere with your body’s ability to deliver normal levels of oxygen to your blood. Some of the most common causes of low blood oxygen levels (hypoxemia) include:
If you have a low blood oxygen level, your healthcare provider will likely have you undergo further testing to determine what is causing your low oxygen levels. A blood oxygen level test alone cannot determine the cause.
The results for a blood sample oxygen level test are usually available right away (within minutes).
A pulse oximeter reveals your oxygen saturation level within seconds.
If you’re using an oximeter at home and your oxygen saturation level is 92% or lower, call your healthcare provider. If it’s at 88% or lower, get to the nearest emergency room as soon as possible.
If you have a chronic lung condition, such as COPD or asthma, you’ll likely need to see your healthcare provider regularly to make sure your treatment is working. If you develop concerning symptoms related to your lung condition, call your provider as soon as possible.
COVID-19 affects people in different ways. Infected people have had a wide range of symptoms — from mild symptoms to severe illness. Some — but not all — people infected with COVID-19 experience low blood oxygen levels. Just because you have a normal blood oxygen level doesn’t mean you don’t have COVID-19 if you’re experiencing other symptoms. Similarly, you could have a low blood oxygen level and not have COVID-19.
The only way to know for sure if you have COVID-19 is to get tested. While an at-home pulse oximeter can be helpful in certain situations, it has limitations and only shows one small aspect of your health. Do not rely on an oximeter to determine a COVID-19 diagnosis.
If you’re experiencing symptoms of COVID-19, contact your healthcare provider as soon as possible.
Symptoms of low blood oxygen levels (hypoxemia) vary depending on the severity of the condition and from person to person. They include:
A note from Cleveland Clinic
Unless you have an underlying health condition that can affect your body’s ability to take in oxygen, it’s not necessary to regularly monitor your blood oxygen level. While using an at-home pulse oximeter can be helpful in certain situations, it’s not as accurate as a blood test to check your blood oxygen levels. If you experience symptoms of low blood oxygen levels or having trouble breathing, be sure to contact your healthcare provider as soon as possible.
Last reviewed by a Cleveland Clinic medical professional on 02/18/2022.
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