Oxygen saturation is the fraction of oxygen-saturated haemoglobin relative to total haemoglobin in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial
blood oxygen saturation levels in humans are 97â100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.