What Is a Pulse Oximeter?

A pulse oximeter is a device that measures your blood's oxygen levels. It is usually placed on your index finger and gives a reading within seconds.

A pulse oximeter, or pulse ox, is a non-invasive electronic device that estimates your blood's oxygen levels. Knowing this measurement, also known as your oxygen saturation, can provide insight into your overall health.

Pulse oximeters can be attached to a number of different body parts including your fingers, toes, nose, forehead, and ears. There are even pulse oximeters built in to some wearable fitness technology

Pulse oximeters are often used in a healthcare setting. A healthcare provider may also recommend you use a pulse oximeter at home. Using a pulse oximeter can help you see when your blood oxygen level is too low, which means your body is working too hard to properly function and you may need to reach out for care or advice.

How Does a Pulse Oximeter Work?

A pulse oximeter is a small device that can clip on to a finger or toe. Some devices have a wire probe that attaches to your finger, toe, or earlobe. Pulse oximeters use light beams to calculate the percentage of your blood carrying oxygen.

Many times, pulse oximeters also measure your pulse. You can check to see if your pulse oximeter is working by taking your own pulse and then comparing it to what the device estimated.

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Why Would You Use a Pulse Oximeter?

Most of the time, pulse oximeters are used in a healthcare provider's office as part of a routine exam. They may also be used in a hospital setting to monitor a patient. For instance, during surgery your breathing and your blood oxygen levels can change. Your healthcare provider may use a pulse oximeter before, during, and after surgery to monitor any change.

There may also be times when it makes sense to use a pulse oximeter at home. Here are some potential reasons why your healthcare provider may recommend that you use a pulse oximeter:

  • You have a condition that impacts your lungs' function. Some examples of conditions that may require you to use a pulse oximeter include chronic obstructive pulmonary disease (COPD), heart failure, COVID-19, asthma, pneumonia, and lung cancer.
  • You are taking a medication to treat a lung disease. Using a pulse oximeter can help both you and your healthcare provider know if the medication you are taking is working or if it needs to be adjusted.
  • You have sleep apnea. Because this condition causes breathing interruptions during sleep, a healthcare provider may want to monitor your blood oxygen saturation.
  • You are planning to start a new workout regimen. Sometimes healthcare providers use pulse oximetry to determine if you can handle increased levels of activity—especially if you have a chronic condition.
  • You have been prescribed oxygen. As your body is adjusting to your oxygen regimen, a pulse oximeter is helpful in letting your healthcare provider know if your oxygen saturation levels fluctuate while you do activities at home.
  • You are flying or spending time at a higher altitude. When you are at a higher altitude, your oxygen needs may increase—which is especially important to be aware of if you are on supplemental oxygen or are traveling to high altitudes.

How to Use a Pulse Oximeter

It is important to follow the manufacturer's instructions, as well as any guidelines from your healthcare provider, when using a pulse oximeter. Overall, they are fairly easy to use.

Editor's Note: Make sure the body part you are using to measure your blood oxygen level is warm. Cold hands or feet, for instance, can cause an inaccurate reading since there is not enough blood being sent to your fingertip. 

Here's how to use a pulse oximeter on your finger:

  1. Make sure your pulse oximeter is set up and has batteries.
  2. Sit down, if possible, to take your reading. Try not to move around too much.
  3. Put your index finger into the pulse oximeter with your fingernail facing up. Your hand should be below your heart.
  4. Wait a few seconds for the screen to show a steady number.
  5. Record your oxygen levels and heart rate.
  6. Report anything abnormal to your healthcare provider or seek immediate medical attention if your reading is exceptionally low.

Editor's Note: Keep in mind that your pulse oximeter may not work well if you have painted nails. The polish can block the oximeter's light used to measure your blood oxygen levels. You'll want to remove any nail polish before taking the reading.

If your oxygen level is lower than you anticipated, try not to panic. Reach out for help and then try to remain calm. You can try getting into a prone position and breathing deeply to improve oxygenation while you wait for help to arrive.

What Is a Normal Pulse Oximeter Reading?

Most pulse oximeters will show two numbers—your pulse and your blood oxygen level. Your oxygen level on the device will be labeled "SpO2." This is measured as a percentage.

Your healthcare provider will let you know what a normal blood oxygen level reading should be for you. Make a note of this number and then contact them if there are any variations when you test.

For most people, a normal blood oxygen level is between 95% and 100%. There are some cases when an acceptable reading may be lower—especially if you have a lung disease like COPD or you are at a higher elevation. But typically, a blood oxygen level that is 92% or lower warrants a call to your provider, while a reading below 88% requires immediate medical attention.

Prescription-based pulse oximeters are usually pretty accurate. Most devices give a reading that is 2% to 4% higher or lower than your actual blood oxygen level. For example, if your oxygen saturation is 94% on your pulse oximeter, it may be actually anywhere from 90% to 98%.

For this reason, the U.S. Food and Drug Administration (FDA) suggests paying attention to trends over time more so than any single reading. If your oxygen level is lower than earlier measurements or is decreasing over time, that could be a sign to reach out to your healthcare provider.

Editor's Note: While it can be a helpful part in flagging potential problems, a pulse oximeter alone is not meant to assess your health or blood oxygen level. You should still be aware of other signs and symptoms of low oxygen levels, such as:

  • Bluish coloring of your skin, lips, or nails
  • Shortness of breath
  • A cough that gets worse
  • Chest pain or tightness

Do Pulse Oximeters Have Limitations?

If you are considering purchasing a pulse oximeter, remember that those you find in your local pharmacy or on the Internet are often labeled "not for medical use." This means the FDA has not reviewed the device's accuracy. Instead, you need to talk with your healthcare provider or a medical supply company about getting prescription-level pulse oximeter for at-home use—especially if you have a chronic condition that requires monitoring.

Pulse oximeters also have a number of limitations of which you should be aware. For instance, the device works by measuring changes in your body’s absorption of red and infrared light, so they can be impacted a your skin color.

In fact, studies have shown that pulse oximeters are less accurate if you are Black, potentially providing an inflated estimate of oxygen saturation levels. This means, when compared to white patients, Black patients received less supplemental oxygen based off their pulse oximeter readings.

Additionally, if you smoke, your reading may be higher than your actual oxygen saturation. This false reading is largely due to the fact that smoking increases carbon monoxide levels in your blood. Pulse oximeters cannot tell the difference between carbon monoxide and oxygen in your blood, so your readings will be off.

There are several other factors that can impact the accuracy of your pulse oximeter as well. These include:

  • Having cold hands
  • Moving while taking your reading
  • Wearing nail polish (especially black, blue, or green)
  • Having artificial nails
  • Experiencing an extremely low oxygen saturation (below 80%)
  • Having thicker-than-normal skin

A Quick Review

A pulse oximeter is a small device that measures the oxygen levels of your blood. Having normal oxygen levels means that your body's organs may not be able to work properly. Healthcare workers can use a pulse oximeter as a routine test during a visit or as part of patient monitoring during a longer stay. It may also be recommended that you use a pulse oximeter at home, especially if you have a chronic condition that could impact your breathing or blood oxygen levels. The pulse oximeter works by being clipped to a part of your body—usually your index finger—and using light beams to measure how much oxygen is in your blood.

Pulse oximeters aren't the be-all and end-all indicator of overall health and blood oxygen, though. For this reason, you should pay attention to any symptoms of low blood oxygen you might have, like shortness of breath or chest pains. Pulse oximeters also have some limitations and can supply false readings if you have darker skin, are wearing nail polish, or are a smoker.

If you are interested in getting a pulse oximeter for use at home, talk to your healthcare provider. With their guidance, you can not only purchase a device that is right for you, but also understand what a normal reading might be for you.

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9 Sources
Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Lung Association. Pulse oximetry.

  2. MedlinePlus. Pulse oximetry.

  3. U.S. Food and Drug Administration. Pulse oximeter accuracy and limitations: FDA safety communication.

  4. American Thoracic Society. Pulse oximetry.

  5. Pulmonary Education and Research Foundation. Pulse oximeters and oxygen saturation.

  6. Indian Council of Medical Research. How to use a pulse oximeter at home.

  7. American Lung Association. Pulse oximetry—A little knowledge can be a dangerous thing.

  8. Sjoding MW, Dickson RP, Iwashyna TJ, Gay SE, Valley TS. Racial bias in pulse oximetry measurementN Engl J Med. 2020;383(25):2477-2478. doi:10.1056/NEJMc2029240

  9. Gottlieb ER, Ziegler J, Morley K, Rush B, Celi LA. Assessment of racial and ethnic differences in oxygen supplementation among patients in the intensive care unitJAMA Intern Med. 2022;182(8):849. doi:10.1001/jamainternmed.2022.2587

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