Pulse Oximetry test is a test that measures how much oxygen is in your blood. It is an easy, painless measure of how well oxygen is being sent to parts of your body furthest from your heart, such as the arms and legs.  A clip-like device called a probe is placed on a body part, such as a finger or ear lobe. The probe uses light to measure how much oxygen is in the blood. This information helps to decide if a patient needs extra oxygen.