fullcortex.net

( 1999 )

-I would like to know what color blood is. I was told that it’s blue but turns red when it comes out. Is there any truth to that?-

The color of blood reflects the condition of the red blood cells (erythrocytes). They contain the oxygen-carrying molecule hemoglobin that is made up of iron and protein. When your blood passes through your lungs, the hemoglobin becomes saturated with oxygen, turning your blood red. As your blood moves through your body and nourishes tissues, the oxygen in it is depleted and your blood is darker red in color. When viewed through the skin, such as the back of your hand, blood in your viens appears bluish.
This color change can be used to indirectly measure oxygen saturation of your blood with an instrument called an oximeter. It can be placed on the tip of your finger or your ear lobe to detect its color, then translate that into a percent of oxygen saturation.
An unusual color change in your blood to a bright red occurs when carbon monoxide combines with hemoglobin. Monoxide binds so firmly with hemoglobin that it can’t carry oxygen. In that circumstance, the blood is not darker in color even when low in oxygen.