Why does the oxygen saturation in the blood only reach 97% and not 100%?

Question

Why does the oxygen saturation in the blood only reach 97% and not 100%?

Answer 1

The reason is that the attachment of oxygen to the iron in hemoglobin is a reversible reaction.  That is, the oxygen can be added and released, which is necessary to deliver the oxygen to the tissues.  The only way that the saturation could be complete is if the oxygen could be added but not released.

Note that the saturation of the hemoglobin by atmospheric oxygen is dependent on the partial pressure of the oxygen in the air.  At higher altitudes, the oxygen partial pressure is lower and the saturation of the hemoglobin is, therefore, lower.  The high saturation that you mentioned in your question happens only at sea level in healthy individuals.

Answer 2

because it isn't only oxygen that gets into the bloodstream. There's probably some carbon monoxide stealing place, and oxygen diffusion in our bodies isn't perfect. It's also being used all the time, decreasing concentration.

Answer 3

The reason is that there is physiological shunting of oxygenated with deoxygenated blood, which happens at the capillary level.

Answer 4

cuz of the carbon dioxide

Answer 5

You may want to make sure the sat monitor you are using is calibrated correctly too..:0)

Answer 6

because you smoke..

it does reach 100%, in healthy individuals with full lung capacity. Normal is 96-100%.. if  you smoke its may be less.