Blood Groups

There are several blood groups. The important blood group system is ABO blood grouping system. The other important blood grouping is Rh-grouping. In both cases, the criterion is the presence or absence of certain antigens on the surface of erythrocytes (RBCs). 

The presence or absence of antigen A and/ or antigen B on the surface of RBCs is the basis of ABO Blood grouping. The following table gives the characteristics of the different blood groups:

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Blood Group     Antigen on RBC     Antibody in Plasma     Can be donated to group(s)

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A                                     A                                  anti-B                               A,O

B                                     B                                  anti-A                               B, O

AB                                A, B                                 nil                               A,B,AB, O

O                                    nil                             anti-A, anti-B                       O

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ABO Blood grouping was discovered by Landsteiner.

O group is called 'Universal Donar' as such individual can donate blood to persons of any blood group. It is due to the absence of antigen on RBC.

AB group is called 'Universal Acceptor' as such individual can take blood of any group. This is because, there is no antibody in this blood group to react with antigens of the donor.

Rh-Grouping:

Rh-antigen is a protein discovered in Rhesus monkeys. Rh-antigen is also present on the surface of RBCs of human beings. About 80% of human individuals have Rh-antigen and they are called Rh-positive. Others, who lack this antigen are called  Rh-negative.

If Rh-positive blood is transfused into an Rh-negative individual, specific anti-Rh-antibodies are formed in the blood of the recipient. If the Rh-negative woman bears an Rh-positive foetus, at the  time of delivery of the first child, when foetal blood comes in contact with the mother's blood, anti-Rh antibodies are formed by the mother's blood. These antibodies  remain in the blood of mother for a long period. If a second Rh-positive foetus is borne by the mother, the anti-Rh-antibodies in the mother's blood enter the foetal circulation and destroy  the RBCs, it results in jaundice and severe anemia in the new born. Such a condition is known as erythroblastosis foetalis.