Blood Groups and Blood Types

Blood is characterized into different blood groups based on the presence or absence of glycoprotein and glycolipid antigens (agglutinogens) on the surface of red blood cells.
There are 24 blood groups and more than 100 antigens
Because these antigens are genetically controlled, blood types vary among different populations.
Classification is based on antigens labeled A, B or AB with O being the absence of the antigens.
An additional antigen, Rh, is present in 85% of humans.

In order to determine a person’s blood type, typing and cross-matching are performed.
A drop of blood is mixed with an antiserum that will agglutinate blood cells that possess agglutinogens that react with it.


Blood plasma usually contains antibodies (agglutinins) that react with A or B antigens. An individual will not have agglutinins against his or her own blood type.