ABO Blood Group System

 

The ABO system was the first human blood group system to be discovered (Landsteiner, 1901)

There are four basic groups within this system: A, B, AB, and O.

The plasma of a person contains natural antibodies to the A or B, if these antigens are absent from the red cells of that person.

 

Blood Group	Antigens on red cells	Antibodies in serum
O	Nil	anti-A, anti-B
A	A	anti-B
B	B	anti-A
AB	A and B	Nil