What Is a Normal O2 Saturation Level?

Oxygen saturation refers to the level of oxygen carried by red blood cells through the arteries and delivered to internal organs. As red blood cells travel through the lungs, they are saturated with oxygen. A low saturation level could indicate a respiratory illness or other medical condition.


Oxygen saturation is measured to determine the severity of an illness and is often the determining factor for treatment. If red blood cells are not adequately transporting oxygen throughout the body, the saturation level falls. Oxygen saturation is measured by pulse oximetry, which uses a sensor of two light sources that haemoglobin absorbs then transmits through the body's tissues. A photodetector picks up the amount of light and converts it to a digital number, which is known as the oxygen saturation level or value.

Normal Ranges

Oxygen saturation level in healthy patients is considered normal between 97 per cent and 99 per cent. Patients who have normal haemoglobin levels can have a saturation level of 95. When the amount of oxygen in the blood is reduced, a condition known as hypoxaemia results, and treatment is then required. In severe cases of hypoxaemia, the patient exhibit a blue tint on his lips, gums, nail beds and around the mouth and eyes. This condition is called cyanosis.


Monitoring oxygen saturation requires a noninvasive monitor that is placed on a finger or toe. Known as pulse oximetry, the probe picks up a measurement of oxygen saturation through the infrared light that passes through tissue.

Other Methods

Oxygen saturation can also be measured through arterial blood gas. Unlike other blood tests, this test takes blood from an artery and measures the amount of oxygen. Arteries carry oxygenated blood away from the heart. A physician might order this test in conjunction with pulse oximetry.


When oxygen saturation levels dip below the normal range, treatment usually involves oxygen therapy. A high concentration of oxygen is delivered by a ventilator through a mask or nasal cannulae (tubes).