Blood oxygen levels refer to the amount of oxygen circulating in the blood. Normal blood oxygen levels fall between 75 and 100 millimeters of mercury (mm Hg) on arterial blood gas (ABG) test results.

A dangerously low oxygen level—usually below 92%—can cause shortness of breath, confusion, chest pain, or fainting. It’s often triggered by lung or heart conditions like COPD, asthma, or heart ...