Human blood can be classified into four groups, as discovered by Karl Land Steiner in 1900. Blood groups are differentiated on the basis of antigens. These antigens are groups of specific molecules produced by and found on the surface of RBCs. There are two types of antigens- A and B. a person’s blood group is A I the antigen present on his RBCs is A, and B if the antigen is B. those whose RBCs have both types belong to the blood group AB. And those who are RBCs have neither antigen, have the blood group O.

Knowing one’s blood group is of vital importance when it comes to serious injuries, illnesses, and operations. In such situations, a person may lose a lot of blood or need to have unhealthy blood replaced. He cannot survive unless he is supplied with healthy blood from another person, a produces called blood transfusion. The patient can receive blood only certain people, depending on the blood groups involved. Similarly, people with certain blood groups cannot donate to everybody. This is because the body rejects blood that has an antigen witch is not production by it. It then regards such blood as a foreign substance that is harmful and produces substances to fight it. This results in a lethal reaction, in which the blood vessels get blocked due to the clumping of RBCs. The following table will give you an idea of blood groups that match

Blood group- Antigen- may donate blood- may receive blood from.

A A A, AB A, O

B B B, AB B, O

AB A+B AB ALL

O NIL ALL O

People with blood group AB can receive blood of all groups and are, therefore, called universal recipients. Those belonging to the blood group O can donate to everyone and are called universal donors.