Medically reviewed by Amelia MacIntyre, DO One of the most important characteristics of blood is its type. Knowing your blood ...

What makes your blood different from someone else’s is your unique combination of protein molecules, called antigens and antibodies. Antigens live on the surface of your red blood cells.

Healthcare professionals classify blood type according to the presence or absence of antigens, which are proteins attached to red blood cells. Of the eight main blood types, AB- is the least common.

ABO blood grouping is based on differences in the type of glycoprotein (protein with carbohydrates attached) present on the surface of red blood cells. Type A individuals have type A glycoproteins; ...