Pulse oximetry measures how much oxygen the haemoglobin in your blood is carrying. Its a simple painless test which uses a sensor placed on your fingertip or earlobe. Oxygen saturation should always be above 95 percent.
Oxygen is carried around in your red blood cells by a molecule called haemoglobin.
Also almost any arterial blood gas analysis will provide the saturation percent for you. Pulse oximetry is a way to measure the amount of oxygen carried by the blood. Pulse oximetry measures how much oxygen the haemoglobin in your blood is carrying. Direct measurement by CO-oximetry.