What is Oxygen Saturation?

Adequate oxygen saturation values are between 95% and 100%. These values can be altered in respiratory illnesses, circulatory problems, or other situations.
What is Oxygen Saturation?
Leonardo Biolatto

Written and verified by the doctor Leonardo Biolatto.

Last update: 27 May, 2022

Oxygen is an essential molecule for most living beings. All the cells in our body use it as fuel to carry out their functions. Therefore, oxygen saturation is a standard that we can measure and is very important.

Oxygen saturation is defined as the fraction of hemoglobin in our blood that is bound to oxygen and therefore carries oxygen. Hemoglobin is a component of our red blood cells that does just that: It transports oxygen to all of our cells.

Measuring this parameter has become an essential step in medicine. This is because, when oxygen saturation levels are below a certain percentage, our life is at risk.

This problem often has to do with respiratory illnesses. For example, coronavirus can alter these levels, complicating the clinical picture.

Therefore, in this article, we’ll explain everything you need to know about oxygen saturation.

What is oxygen saturation?

As we’ve already mentioned, oxygen saturation is a parameter that refers to the percentage of hemoglobin that’s bound to oxygen. This percentage can vary depending on many aspects, such as respiratory function.

Normal saturation values fall between 95% and 100%. This is because, when we saturate below 89%, our cells can’t perform their functions properly.

In fact, if oxygen saturation levels drop for a short period of time, there need not be any damage to our organism. However, if this situation persists or repeats, it does have consequences for the tissues in our body.

When oxygen saturation drops, we enter a state called hypoxemia. This is the medical way of saying that blood oxygen levels are below normal. It usually has to do with circulatory or respiratory problems.

Red blood cells.
Hemoglobin is inside the red blood cells, and from there, it transports oxygen in the body.

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How is oxygen saturation measured?

Currently, there are different ways to measure oxygen saturation. The most common and accessible means is through the use of a device called a pulse oximeter. It’s a small clamp-like device that can be placed on a finger or toe.

The pulse oximeter emits beams of light that pass through the blood and measure oxygen levels through the skin. Its mechanism of operation is complex, but it allows us to measure both saturation and heart rate.

Another way of measuring oxygen saturation is through arterial blood gases. This technique involves drawing blood from an artery. Unlike the pulse oximeter, this technique allows for the measuring of other values, such as the percentage of carbon dioxide or blood pH.

However, although blood gas analysis is a more complete test, it’s also more complex and invasive. Therefore, as a rule, the pulse oximeter is the most common, as it’s quick and painless.

A doctor measuring a patients oxygen saturation.
The pulse oximeter allows for painless and fast measurement.

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What happens in situations of hypoxemia?

Hypoxemia can occur for several reasons. First, because there’s not enough oxygen in the air we’re breathing. It also depends on our lungs being able to perform their function properly. That is, that they inhale oxygen correctly and eliminate carbon dioxide.

In addition, hypoxemia can be caused by a circulatory problem. The blood must be able to reach the lungs and pick up oxygen to transport it to all parts of the body. Some specific causes are asthma or heart disease.

The most typical symptom of low oxygen saturation is shortness of breath. Headache, dizziness. and weakness may also occur. If the situation is prolonged, confusion and disorientation may also occur.


In principle, a healthy person doesn’t need to have a pulse oximeter at home or monitor their oxygen saturation. However, it’s a basic measurement at any level of medical care, especially if there’s a respiratory or blood problem.

The utility that these small, portable devices have brought to medical care allows for improved early diagnosis. At a glance, the physician can have important information to define treatment or hospitalization.

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