Oxygen Saturation and How It Is Tested

What Levels Are Normal and How to Raise Them

Oxygen saturation, or "O2 sat" for short, is a measure of how much oxygen is in your blood. For most healthy adults, a normal oxygen saturation level is between 95% and 100%.

An oxygen saturation reading below this requires medical attention because it means your body isn't getting enough oxygen to function properly.

This article covers conditions that affect the amount of oxygen in your blood and the complications of having low oxygen saturation. You will also learn how to measure your blood oxygen levels at home (if recommended) and when to seek treatment.

Verywell / Laura Porter

How to Measure Oxygen Saturation

Oxygen saturation is measured in one of two ways: an arterial blood gas test (ABG or Sa02) or pulse oximetry (Sp02).

ABG is usually only done in a hospital, while pulse oximetry can be done in other healthcare settings (like a provider's office) and even at home.


An ABG value refers to the levels of oxygen and carbon dioxide in blood running through your veins.

During an ABG, a nurse or lab technician draws blood from an artery, such as the radial artery in the wrist or the femoral artery in the groin. The sample is immediately analyzed by a machine or in a lab.

Your ABG value can give your healthcare provider a sense of how efficiently your hemoglobin—the protein in red blood cells that transports oxygen throughout the body—exchanges oxygen and carbon dioxide.

Pulse Oximetry

A pulse oximetry reading reflects the percentage of oxygen saturation in arterial blood.

Unlike the ABG test, pulse oximetry does not involve a needle. Instead, the test uses a sensor to read wavelengths reflected from the blood.

The probe is attached to your finger, earlobe, or another place on the body. A pulse oximeter can give results on a screen in just a few seconds.

If at-home monitoring is recommended, you can check your oxygen saturation levels using wearable pulse oximetry devices. Even some smartwatches even have this feature. You can also buy a pulse oximetry device at your local pharmacy or online.

Oxygen Saturation Levels
Reading ABG Level O Sat Result
Below Normal < 80 mmHg  < 95%
Normal > 80 mmHg 95% to 100%

What Causes Low Oxygen Saturation?

A drop in oxygen saturation in the blood is called hypoxemia.

It can be caused by situational factors, like:

  • Less oxygen in the air (for example, when you are flying in an airplane)
  • Breathing in carbon monoxide, cyanide, or another substance that binds more strongly to hemoglobin than oxygen does

Conditions that affect breathing, oxygen absorption, and red blood cell or hemoglobin count can also cause low O2 sat.

Conditions That Affect Oxygen Saturation

Blood disorders, problems with circulation, and lung issues can prevent your body from absorbing or transporting enough oxygen. When this happens, it can lower your blood's oxygen saturation level.

Examples of conditions that can affect your oxygen saturation include:

  • Respiratory infections (e.g., a cold, the flu, COVID-19): Any condition that affects your ability to breathe will affect your oxygen intake
  • Chronic obstructive pulmonary disease (COPD): A group of chronic lung diseases that make it difficult to breathe
  • Asthma: A chronic lung disease that causes airways to narrow
  • Pneumothorax: A partial or total collapse of the lung
  • Anemia: Not having enough healthy red blood cells
  • Heart disease: A group of conditions that affect the heart's function
  • Pulmonary embolism: When a blood clot causes blockage in an artery of the lung
  • Congenital heart defects: A structural heart condition that is present at birth

Complications of Low Oxygen Saturation

Every cell in your body needs oxygen to work. Low oxygen saturation in the blood can mean there's less oxygen in the body's tissues, including the organs and muscles. When this happens, it's called hypoxia.

Your cells can adapt to a lack of oxygen when the deficiency is small. However, with larger deficiencies, cell damage and cell death can happen.

Hypoxia usually happens because there is not enough oxygen in the blood (hypoxemia). However, it can also happen when:

  • There are not enough red blood cells to carry oxygen to the tissues due to severe bleeding, after a trauma, or conditions like sickle cell anemia.
  • There is inadequate blood flow due to a stroke, in which there is low blood flow to a region of the brain, or a heart attack, in which there is low blood flow to the heart muscles.
  • The tissues require even more oxygenated blood than can be delivered due to severe infections that cause sepsis, which may result in hypoxemia and eventually organ failure.

Treating Low Oxygen Saturation

Generally speaking, an oxygen saturation level below 95% is considered abnormal. This should be evaluated by a healthcare provider. An oxygen saturation level below 90% requires emergency medical attention.

The following can help raise blood oxygen fast:

  • Sit up straight rather than laying flat.
  • Get some fresh air or go inside if you are outdoors and it is very hot/very cold.
  • Cough to loosen up any mucus (like from allergies or a cold/the flu).
  • Be sure that you are taking deep, full breaths to get oxygen into your blood.

But if someone's oxygen saturation is dangerously low, they will need oxygen therapy—sometimes urgently.

The brain is the most susceptible organ to hypoxia. Brain cells can begin to die within five minutes of oxygen deprivation. If hypoxia lasts longer, it can lead to coma, seizures, and brain death. It is very important to find out the cause of low oxygen saturation so the problem can be fixed.

The full treatment plan will depend on the cause of the low saturation levels. For example:

With chronic conditions like COPD and asthma, the cause of hypoxia is usually low air exchange in the lungs and alveoli. In addition to oxygen therapy, steroids or rescue inhalers (bronchodilators) might be needed to open the airways.

In circulatory conditions like heart disease, impaired blood flow reduces oxygen delivery. In this case, medications that improve heart function, such as beta-blockers for heart failure or prescription medications to treat heart arrhythmias, can help improve oxygen saturation.

With anemia, the blood supply to the tissues is reduced because there are not enough healthy red blood cells with hemoglobin to carry oxygen. Sometimes, a red blood cell transfusion is necessary to increase a person's level of healthy red blood cells.


Oxygen saturation is the measure of how much oxygen is traveling through your body in your red blood cells. Normal oxygen saturation for healthy adults is usually between 95% and 100%.

If you have a chronic health condition that affects your lungs, blood, or circulation, regularly tracking your oxygen saturation may be recommended. An oxygen saturation level below 95% is not normal. A level under 90% requires emergency care.

Frequently Asked Questions

  • What is a dangerously low oxygen saturation level?

    A saturation level of 90% is usually considered the point where your oxygen saturation is dangerously low and you should get immediate medical attention. However, if you have pneumonia or another active infection or medical issue, your doctor may direct you to go to the emergency room if it is 92% or lower.

  • Which finger is best for an oximeter?

    Most oximeters work best when used on the middle finger. Some studies have shown that the right middle finger works best. In some people, the right thumb may also work well.

  • How long does it take for oxygen levels to return to normal after COVID?

    COVID-19 can damage your lungs and affect your breathing. A lot of people who have COVID experience low 02 sats—sometimes dangerously low. We are still learning about how COVID affects the lungs. It can take months for the lungs to heal after COVID. Some people develop lasting breathing problems after they have the infection.

  • What is a normal O2 sat for a child?

    Normal oxygen saturation levels are the same for kids as they are in adults; between 95% and 100%.

  • What oxygen level is normal while sleeping?

    Oxygen levels above 90% are normal when you're asleep. If your oxygen saturation levels are lower than that while you're sleeping, it could be a sign that you have a disorder like sleep apnea.

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Verywell Health 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.
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By Deborah Leader, RN
 Deborah Leader RN, PHN, is a registered nurse and medical writer who focuses on COPD.