In ABO blood group system, an individual can be blood group A, B, AB or O based on the types of antigens on the surfaces of red blood cells.
Blood group A
An individual with blood group A has A antigens on the surfaces of red blood cells and antibodies against B antigens in plasma.
Blood group B
An individual with blood group B has B antigens on the surfaces of red blood cells and antibodies against A antigens in plasma.
Blood group AB
An individual with blood group AB has both A and B antigens on the surfaces of red blood cells. An individual with blood group AB is a universal recipient.
Blood group O
An individual with blood group O has both antibodies against A and B antigens in plasma. An individual with blood group O is a universal donor.