What is the basis of grouping blood into different types?

Everybody cannot receive blood from all blood groups. Why?

Antigen is the molecule capable of inducing the immune response to the host organism. Antigens are targeted by the army of proteins called antibodies. Each antibody is produced by the immune system that bond in a specific fashion with antigens. Several antigens are possessed by a membrane of red blood cells. Main two blood grouping which is widely used are ABO and Rh.

ABO blood grouping

ABO blood grouping system is one of the most common type of blood grouping. ABO blood groups are controlled by gene I.

ABO blood grouping mainly based on the presence or absence of antigen A and antigen B on the surface of red blood cells.

Rh grouping

Another antigen Rh factor is present in the membrane of the red blood cells. People who have these antigens are called Rh +ve and the people who do not have these antigens are calked Rh-ve.

Everybody cannot receive blood from all blood groups because when foreign antigen reaches to the blood, it starts its defense activity. The antigen present in the received blood and antibody in the recipient's blood will react with each other and form a blood clot.

For example, if donor blood group is A and recipient blood group is B, then the recipient's antibodies attach to donor red blood cells and cause clumping which may cause hemolysis.

Similarly, if Rh—ve person exposed to Rh+ve blood then it will form antibodies against the Rh antigens.