Blood typing is a method to tell what specific type of blood you have. What type you have depends on whether or not there are certain proteins, called antigens, on the red blood cells or if there are antibodies to these substances.
Blood is often grouped according to the ABO blood typing system. on This method breaks blood types down into four categories:
Type A Type B Type AB Type O
Your blood type (or blood group) also depends on what has been passed down to you from your parents.
<haematology> The major human blood type system which describes the oligosaccharide glycoprotein antigens found on the surface of human blood cells.
According to the type of antigen present, a person may be assigned a blood type of A, B, AB or O. A second type of antigen, the Rh factor, renders a positive or negative blood type. The ABO blood group system is important because it determines who can donate blood to or accept blood from whom.
Type A or AB blood will cause an immune reaction in people with type B blood and type B and AB blood will cause a reaction in people with type A blood.
Conversely, type O blood has no A or B antigens, so people with type O blood are universal donors.
And since AB blood already produces both antigens, people who are type AB can accept any of the other blood types without suffering an immune reaction.