Blood Transfusion & the ABO Rhesus System

Applied Science: BTEC Level 3 National Extended Diploma, topic 4.5.3

Blood Transfusion & the ABO Rhesus (Rh) System

There are many different blood types. Blood types need to be matched prior to blood transfusions to prevent rejection.

Red blood cells are coated in antigens made of glycolipids and glycoproteins.
The composition of these molecules is determined by genetics, which has evolved over time.
The two most well known blood groups are the ABO and Rh systems.

The surface antigens in the ABO blood group are glycolipids, called antigen A and antigen B.
People with blood type A have antigen A.
Those with blood type B have antigen B.
Those with blood type AB have both antigens.
People with blood type O have neither antigen.
The glycoproteins serve as antigens and can elicit an immune response in a person who receives a transfusion containing unfamiliar antigens.

Individuals with blood type A have antibodies against the B antigen, and vice versa.
Type O blood has antibodies against antigen A & B.
Type AB blood doesn't have antibodies against either antigen.
When type A and type B blood are combined, the antibodies in the plasma bind with the opposing antigen.
This causes clots that coagulate in the kidney causing kidney failure.
So, individuals with antibodies against a blood antigen can't be given that blood type.

Type O blood, which has no A or B antigens, does not elicit an immune response when injected into a person of any blood type.
So, O is considered the universal donor.
Persons with type AB blood can accept blood from any blood type.
So, type AB is considered the universal acceptor.

Most people have the Rh antigen (Rh+) and do not have anti-Rh antibodies in their blood.
The few people who do not have the Rh antigen and are Rh– can develop anti-Rh antibodies if exposed to Rh+ blood.
This can happen after a blood transfusion or after an Rh– woman has an Rh+ baby.
The first exposure does not usually cause a reaction.
At the second exposure, enough antibodies have built up in the blood to produce a reaction that causes agglutination and breakdown of red blood cells.