A pulse oximeter is a handy medical device that uses two frequencies of light – red and infrared – to determine the percentage of hemoglobin in the blood that is saturated with oxygen, otherwise known as your oxygen saturation level (O2 sat level). If you have ever been in a doctor’s office and heard your health care providers talking about SpO2 and SaO2, you might be left wondering, “What is SpO2 and how is it different from SaO2?” When oxygen saturation is measured using a pulse oximeter, it is referred to as SpO2, which stands for percutaneous oxygen saturation. When it is measured by way of a blood test known as an arterial blood gas study, it is referred to as SaO2, or arterial blood oxygen saturation.
Your oxygen saturation level is dependent upon a number of factors including your health condition, breathing rate and activity level. When measured by pulse oximeter, normal oxygen levels range between 95-100%. O2 sat values under 90% are considered low. When measured by arterial blood gas analysis, a typical healthy O2 saturation is generally between 75-100 mm Hg.
If one or both of your oxygen saturation readings fall below healthy O2 saturation levels, oxygen therapy will likely be recommended. Supplemental oxygen is generally covered by Medicare and other insurance companies when your oxygen saturation level, as measured by pulse oximetry, is at or below 88% at rest and/or your partial pressure of oxygen (Pa02), as measured by arterial blood gas study, is at or below 55 mm Hg.
A pulse oximeter can be a useful and reassuring tool if you are using home oxygen therapy. Not only will using a pulse oximeter at home help you better manage your health condition by allowing you to track your oxygen saturation throughout the day, but it will allow you to properly measure and adjust your oxygen flow rate – under the strict guidance and direction of your doctor only – according to your activity level. If you think you need to adjust your flow rate or the frequency or amount of oxygen you receive, talk with your doctor first and record your fluctuating O2 saturation. Never adjust your flow rate or the amount of oxygen you receive on your own.
You can purchase a home oximeter either online, from a reputable supplier like Inogen, or from a medical supply company or pharmacy. Most models made for in-home use are inexpensive and easy to use so you can track your oxygen saturation level on your own. Simply attach the pulse oximeter probe to your finger and wait until the LED screen indicates your SpO2. It should only take a couple of seconds. The pulse oximeter will also measure and display your heart rate. You may want to record your daily SpO2 readings in a health journal or on a piece of paper to later show your health care provider, particularly if you are experiencing O2 sat fluctuations throughout the day. This way, your doctor can determine if your oxygen flow rate is meeting your needs properly during all of your activities.
It is important to know your oxygen saturation level if you have a health condition that affects how much oxygen is in your blood. When your blood oxygen level is low, the cells and tissues of your body receive less oxygen, which means your body cannot function the way it should. This can negatively impact all your bodily functions and can also put a strain on your heart and your brain.
According to the American Thoracic Society, most people need an oxygen saturation level of at least 89% to keep their cells healthy. Having a blood oxygen level lower than this for short periods of time is not believed to be dangerous. However, your cells and tissues may become damaged if your oxygen saturation level runs low many times or continuously.2 As such, anyone with a lower oxygen saturation or with an O2 sat that drops during certain activities, like exercise or sleep, should be monitoring their O2 saturation regularly.
To get the most accurate O2 sat reading from your pulse oximeter, there needs to be enough blood flow to the hand and finger wearing the device. This means the best reading occurs when your hand is warm, relaxed and below the level of your heart.2
Most oximeters are reasonably accurate, giving you a reading of 2% over or 2% under what your oxygen saturation would be if measured by an arterial blood gas study.2 A pulse oximeter reading may be less accurate, however, if any of the following apply:
Because SpO2 levels vary from person to person, the best way to ensure you are getting accurate readings is to begin by recording your oxygen saturation level at rest and at different activity levels over a period of time. Getting a baseline O2 saturation allows you to see your typical range throughout the day, which then allows you to see when there are any abnormal drops in your SpO2. Generally speaking, a drop of about 3 or 4% from your usual oxygen saturation is a concern.
An inaccurate pulse oximetry reading can be misleading and alarming. To get the best oxygen saturation reading possible, consider the following tips:
It is also important to know how to read your pulse oximeter correctly. Your pulse oximeter takes two readings, so it is critical that you know which is which and do not mix up the two. So, what are the two readings on a pulse oximeter? This device measures both your pulse rate and your blood oxygen saturation. Usually, your pulse rate appears on the device first and may be indicated by a small heart or another symbol. Your blood oxygen saturation, which may be labeled as your SpO2, will usually appear second.
Keep in mind that a normal heart rate typically falls between 60 and 100 beats per minute, while a normal oxygen saturation rate should be between 95-100%. If you have a weak or irregular pulse, your pulse oximeter may not sense it properly. If your numbers are worrisome, try waiting a few minutes, making sure your hands are warm, and try again on another finger.
SpO2 is a measure of the amount of oxygen-carrying hemoglobin in your blood as measured by a pulse oximeter. This oxygen saturation measurement tells you whether your body is getting the oxygen you need and, particularly for people who struggle with maintaining normal O2 saturation, knowing your SpO2 could help prevent hypoxia and hypoxemia.
Your oxygen saturation level tells you whether you are getting the oxygen you need for your body to function properly. A healthy person’s normal O2 saturation reading should fall between 94 and 99%. If your oxygen saturation is below 90%, it is likely that your doctor will recommend supplemental oxygen to improve your O2 sat levels and provide your body with the oxygen it needs. For people with chronic lung diseases like COPD, however, their normal oxygen saturation may be lower than the usual range. It is good to be aware of this, and it is still important to watch for significant fluctuations (specifically, drops of 3-4% or more).
Your oxygen saturation can drop for any number of reasons, depending on your overall health, activity level, location and breathing. Some very normal activities, like sleeping, can cause your O2 saturation to drop, though your O2 sat levels are likely to remain within the normal range. Changes in oxygen availability, as experienced in an airplane or at high altitudes, can also cause drops in your oxygen saturation level. If you have a lower concentration of hemoglobin, like those with iron deficient anemia have, you may also experience lower O2 saturation. Finally, illnesses and conditions that affect your breathing, your lungs’ ability to absorb enough oxygen or that cause problems with gas exchange within the body can cause significantly lower oxygen saturation.
Pulse oximeters take two readings, measuring both your blood oxygen saturation and your pulse rate. Typically, the first number you will see is your pulse rate. While pulse oximetry is primarily used to measure your oxygen saturation, knowing your heart rate can help determine potential problems. In many cases, your pulse rate gives information about how much oxygen your body is receiving, as well as whether your heart and lungs are working the way they should and getting the blood they need. The second number you will see, your blood oxygen saturation, tells you how much oxygen the hemoglobin in your blood is carrying. This indicates whether you’re getting the oxygen you need throughout your body. A pulse oximeter can gives you a picture of your oxygen saturation and pulse rate right in that moment, which can be quite helpful information.
 “Hypoxemia (Low Blood Oxygen).” Mayo Clinic, Mayo Foundation for Medical Education and Research, 1 Dec. 2018, www.mayoclinic.org/symptoms/hypoxemia/basics/definition/sym-20050930.
 Fahy, Bonnie, et al. “Pulse Oximetry.” ATS Patient Education Series, American Thoracic Society, Updated Mar. 2018, https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf.
 “How a Pulse Oximeter Works.” COPD Foundation, COPD Foundation, 23 Jan. 2020, www.copdfoundation.org/COPD360social/Community/COPD-Digest/Article/309/How-a-Pulse-Oximeter-Works.aspx.
Hegg, Jessica. “Understanding SpO2 and Normal Oxygen Levels.” HomeCare Magazine, Cahaba Media Group, Inc., 28 Sept. 2016, www.homecaremag.com/understanding-spo2-and-normal-oxygen-levels.
Leader, Deborah. “Understanding Oxygen Saturation.” Verywell Health, About, Inc., 7 May 2020, www.verywellhealth.com/oxygen-saturation-914796.