Human Blood Group

Human Blood Group

When the amount of blood is low or the blood is needed for some reasons, then blood is donated to sick persons from the healthy persons. Blood donating and receiving person should have the same group of blood. It is seen that the blood of donor and receipient normally gets mixed outside the body. But in some cases the blood of donor and receipient does not get mixed, instead the blood coaguletes. Before knowing of about blood coagulation, we have to know about Antigen and Antibody. If an unexpected protein comes into the blood, a special type of chemical is formed which reacts with the external protein. This substance created by blood is called the antibody. Large amount of antibody is created in blood. The external protein which influences to create the antibody in the blood is called the antigen. When antigen and antibody come to the same solution, a special type of reaction occurs that is called the antigen antibody reaction. In the case of blood cell for the reaction of antigen and antibody the blood corpuscles change into clusters. In 1900 Dr. Karl Landsteiner while working in a medical laboratory saw that when the blood corpuscles of one person are mixed with the blood of another person the blood corpuscles coagulate. He did more experiments on this matter and found that there are two types of antigen in blood cell and in the same way two types of antibody in the serum.

For easy understanding, these two types of antigens are named as A and B. Human beings have any one or both of the antigens or no antigen in their blood. There are four types of blood according to the type of antigen they contain. The human beings who have the antigen A are called the group A, who have the antigen B are called the group B, who have both the antigen A and B are called the AB group and who have no antigen is called the O group. The types of antigen in blood cell must not be the same antibody in serum. It is clear that, if an A antigen carrier in serum has the antibody A then the blood gets clotted and causes death. So A blood group persons have the antigen A and no antibody against it, but there are no B antigen in their body but contain B antibody. The antibody in the blood are called the α (Alpha or anti A) or β (Beta or anti B). Thus, based on the presence of antigen and antibody, the blood of all the human beings are divided into four groups A, B, AB and O.

The table bellow shows that the relation of A, B, O blood group and the relation of donor and recipient.

Blood Group	Antigen in RBC	Antibody in plasma	The group to which can be donated	The group from which can receive
A	A	Anti-B	A and O	A, O
B	B	Anti -A	B and O	B , O
AB	A,B	No Antibody	AB	A, B , O and AB
O	No Antigen	Anti – A, B	A, B , O and AB	Only O

Antigen is called the Aglutinogen and the antibody is called the Aglutinin. Antigen or aglutinogen stays outside the plasma membrane of RBC. Antibody or aglutinin stays in plasma. Near about 42% of human beings have the blood group ‘A’, 9% have ‘B’, 3% have ‘AB’ and 46% have ‘O’.

It is clear from the above table that the antigen which is not present in the blood only that antibody will be found there. That is, blood group A has the A antigen, B has the B antigen, AB has both A and B antigen. None of them has the same type of antibody. As there is no antigen in blood group O, it contains both the antibody A and B. The antibody of group A clots the RBC of group B, on the other hand, the antibody of group B clots the RBC of group A. But blood group AB cannot clot the RBC of other groups because there is no antibody in this group. The O group blood clots the other three groups of blood but not its own group because this group has two types of antibody. So the O group can only receive the blood of group O but it is able to donate blood to all the groups. It is clear from the table that the group A can donate blood to the A and AB. In the same way the group B can donate blood to the group B and AB. The group AB can receive the blood of all the four groups -- A, B, AB and O. That is why AB group is called the universal receipient. In the same way any group can receive the blood of group O. That is why no blood test is required. O group is called the universal donor.