How to Measure SpO2

When we breathe in oxygen, it is inhaled by the lungs and goes into the bloodstream. The amount in the bloodstream at any time is known as the body’s blood oxygen level, and it plays a significant role in the proper functioning of the body’s vital organs. 

People with lung and heart conditions can have issues maintaining normal blood oxygen levels, so there are effective ways to measure the body’s SpO2 to reduce the risk of harm or danger from a low level.  

If you aren’t sure if you should be measuring your SpO2 levels or what you should be looking for, this post can help. 

Keep reading to know how to measure SpO2, the best ways to maintain a normal blood oxygen level, and the factors that can affect a SpO2 measurement. 


What Is SpO2?


To understand how to measure SpO2, you should first understand what SpO2 is and its vital role in the human body.


Also known as oxygen saturation, SpO2 is the amount of oxygen-carrying hemoglobin in a person’s blood in relation to the total hemoglobin in the blood. The human body and its organs require a precise balance of blood oxygen saturation to function properly. Blood oxygen saturation affects many processes and functions within the body, from digestion to cognition, hence the importance of normal SpO2 levels.   


Additionally, the cells need oxygen to create energy, which the body needs to effectively complete all its processes. Maintaining normal oxygen saturation levels is essential to the body’s continued survival.


The SpO2 level is read as a percentage and typically ranges between 95% and 100%, while as low as 92% is still considered a normal, healthy range in certain individuals. 


SpO2 stands for:






Pulse oximetry is a method of measuring how much oxygen saturation there is in the blood and how efficiently it is carried into the farthest extremities of the body, including the arms and legs.


How to Read an SpO2 Monitor


Pulse oximeters are medical devices that measure oxygen saturation in a patient’s blood. They can help monitor the health of someone who has difficulty breathing or people with certain conditions.


SpO2 monitors use light to measure the level of oxygenated hemoglobin, which is better for tissue than carbon dioxide-laden hemoglobin. There are two types of pulse oximeters: a digital and an analog model. 


A digital one uses a sensor that records and displays the blood oxygen saturation (SpO2) and pulse rate (P). An analog model does not have a sensor but measures the SpO2 by obtaining light through the fingers or earlobe. The oximeter also records the pulse rate and temperature.


The SpO2 monitor reflects the percentage of hemoglobin molecules that are carrying oxygen. The higher this value is, the better your body will be able to utilize oxygen. A SpO2 of more than 95% is considered good. A low SpO2 value indicates poor oxygenation either due to breathing problems or serious health problems, such as anemia or pneumonia. The second component of a pulse oximeter is the P. The P indicates how many times the heart beats per minute (bpm). It ranges from 40 to 210 bpm, with 120 bpm being the average.


How to Measure SpO2 at Home


Measuring oxygen levels is done quickly at home and is essential for patients with diseases that impact lung function. These include COPD, pneumonia, lung cancer, heart failure, and COVID-19. 


Patients with lung diseases should measure their SpO2 levels to evaluate how well the treatment is working and monitor their overall health. 


The following are other conditions that may require SpO2 monitoring:

  • Asthma
  • Cystic Fibrosis
  • Smoke inhalation injury
  • Head or neck injury that impedes breathing


How to Use a Pulse Oximeter to Measure Oxygen


Using a fingertip pulse oximeter to measure blood oxygen saturation levels only takes a few minutes and can be done at home or anywhere you can sit down for a few moments. The small, electronic device is clipped onto a body part, usually a fingertip.

The device emits an infrared light that passes through the finger and blood, while a sensor on the other side of the finger measures how much light passes through without getting absorbed by the tissue and blood.

The fingertip pulse oximeter is a very accurate method of measurement, typically within 2% to 4% of the actual blood oxygen saturation level. It also measures heart rate.

Measurements between 96% and 99% indicate a healthy amount of oxygen-carrying hemoglobin in the blood.


We carry an alternate to the Nonin ONYX II 9550 and ONYX VANTAGE 9590 oxiemters with a 0.1% perfusion rate, check out our part 11931. If you are looking for an alternative to the Masimo MightSat check out Cables & Sensors part 11930 with a 0.025% low perfusion rate.


Other Ways to Measure SpO2


Many over-the-counter pulse oximeters are not FDA-approved and must not be used for medical purposes. However, they’re perfectly okay for fitness, sports, and aviation applications. There are also other ways to measure SpO2 with less margin of error.

One is an arterial blood gas test, where a blood sample is taken from the wrist. A blood draw test provides much more information about oxygen levels than an oximeter, but the oximeter provides much quicker results.

Nowadays, smartwatches and fitness trackers also have SpO2 sensors that measure blood oxygen saturation. Although their technology is not as accurate as pulse oximeters and medical-grade SpO2 sensors, it’s helpful for monitoring blood oxygen levels on the go.


Factors That Affect an SpO2 Measurement


There are a few factors that can impact oxygen saturation. 


When measuring blood oxygen saturation, the bright ambient lighting in the area around you can dilute the infrared lighting from the oximeter, giving an inaccurate reading. 


When placing the pulse oximeter on the finger, ear, or toe, ensure the device is put on correctly, secured, and not resting on another body part. If the device is too loose, it may be unable to get an accurate measurement. 


When measuring from the finger, ensure your wrist area has proper blood flow to read the oxygenized blood cells correctly.


Some medications can affect a SpO2 measurement, such as blood-thinning or nerve-blocking medications. Be aware of your medications when measuring your oxygen saturation levels.


Too much movement during a reading can also impact the speed of blood flow, garnering incorrect readings. Sitting still during a reading is highly recommended to allow the device to work properly. 


Other factors include having nail accessories on your fingertip during a measurement or being in high altitudes, where the air has less oxygen. 


Tips on How to Measure SpO2 at Home


  • Check SpO2 levels throughout the day to monitor and keep an eye on measurements during physical activity.
  • Keep a log or journal of daily readings so you can quickly reference them with your doctor.
  • Contact your doctor immediately if your levels drop below what is considered your “normal.”
  • Despite what your measurements read, pay attention to how you feel throughout the day. If you feel symptoms of low blood oxygen levels, such as severe shortness of breath, contact your doctor.


What Is a Normal Blood Oxygen Level?


Most healthy people have a blood oxygen saturation level between 95% and 100%. Patients with lung diseases (like COPD) may have a lower blood oxygen saturation level. 

If you have an underlying condition, your doctor will work with you to determine your normal blood oxygen level. For example, patients with severe COPD often have a much lower normal blood oxygen level, ranging from 88% to 92%.


How the Body Maintains Normal SpO2 Levels


The human body does most of the work to maintain normal oxygen saturation levels through breathing. Every time you take a breath, oxygen rushes into the lungs, which binds to the hemoglobin molecules inside the red blood cells. Then the oxygen is transported to different body parts through the red blood cells.


The human body is typically capable of maintaining healthy, balanced oxygen levels, even during exercise, when the body is under stress or at higher altitudes. 


Here are other ways you can achieve healthy levels of SpO2:

  • Walking outside during the day
  • Breathing exercises to open the airways 
  • Opening the windows to let fresh air circulate indoors
  • Quitting smoking to improve breathing and circulation 
  • Adding plants to interior spaces that release oxygen


What Happens if I Have Low Oxygen Levels?


Low levels of SpO2 can result in severe symptoms and serious complications and should be addressed immediately by a doctor. 


The human body and its organs need oxygen to function properly. When the transport of oxygen is seriously affected, the organs face potential danger should medical intervention not happen quickly. 


You should contact your doctor immediately if you get a pulse oximeter reading of less than 92%. This could be a sign of hypoxemia, occurring when oxygen levels in the blood are dangerously low. Asthma, heart disease, and even high altitude can lead to hypoxemia.


If left untreated, hypoxemia can result in hypoxia, which occurs when the oxygen levels in the tissues are too low, resulting in confusion, bluish skin, and changes in breathing and heart rate. 


Prolonged hypoxia can cause organ damage and brain and heart damage, which can lead to death if not treated properly. 


If blood oxygen saturation levels fall below 88%, seek immediate medical attention.


Should I Use a Pulse Oximeter?


Pulse oximeters are a noninvasive, easy way to check if you have normal oxygen saturation levels quickly. There’s no harm or risk in measuring SpO2 even if you are healthy, and it is an effective way of monitoring your body’s blood oxygen levels on a long-term basis. 


If you have a heart or lung condition, your doctor will likely want you to use a pulse oximeter to monitor your oxygen levels at home. 




Measuring SpO2 levels at home can be easily managed with a fingertip pulse oximeter. Whether you have a lung condition that requires monitoring or you want to be aware of your daily levels, monitoring your blood oxygen saturation levels is simple and effective.