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Knowledge Centre - Blood Groups

Blood Groups

During life-saving blood transfusion, it is very important that the blood unit of the appropriate blood group is provided. In other words it is important that the blood group of the donor is compatible with that of receiver. Understanding of blood groups, therefore, becomes very important. This important, path-breaking discovery of Blood Groups was made by Dr. Karl Landsteiner, for which he was awarded the Nobel Prize.

In broad terms, people all over the world can be classified into eight blood groups. This classification is on the basis of two systems:

a. The A, B System
After studying the population, Dr. Karl Landsteiner found the existence of Antigen A and Antigen B on the outer membrane of the R.B.Cs in the blood. Every person in the world either had Antigen A, or Antigen B, or both of them, or neither of them. By this system people were classified as:

iA  if only Antigen A was present
iiB  if only Antigen B was present
iiiAB  if both Antigen A & B were present
ivO  if both Antigen A & B were not present

b. The Rhesus System
Landsteiner further discovered the existence of another Antigen called Rhesus Antigen. This Antigen, which again was found on the outer membrane of the RBCs, either existed in a person’s blood or did not exist. People were classified, by this system, as:

i Rh. Positive  if Rhesus Antigen was present
ii Rh. Negative  if Rhesus Antigen was not present

Almost 85 - 90 % of people in the world have the Rhesus Antigen in their blood. Thus a person who is ‘Rh Negative’ can consider oneself to belong to a rare group. It may be advisable for each person with a negative blood group to maintain a list of persons with the same blood group.

A combination of the above two systems results in people all over the world being classified into the following eight (8) blood groups:

Sr.No. Blood Group Common
Antigen A Antigen B Rhesus
1 A Rh Positive A+ve present absent present
2 B Rh. Positive B+ve absent present present
3 AB Rh Positive AB+ve present present present
4 O Rh. Positive O+ve absent absent present
5 A Rh Negative A-ve present absent absent
6 B Rh. Negative B-ve absent present absent
7 AB Rh Negative AB-ve present present absent
8 O Rh. Negative O-ve absent absent absent

While transfusing blood, it is ensured that the blood group of the donor matches that of the receiver. Cross-matching is carried out to ensure that compatible blood is given to the receiver.

Who can give to whom?

While transfusing blood, the donor’s blood should not contain any Antigen that is foreign to the recepient’s blood. On this basis, the following table shows ‘who can give to whom’:

Recipient A+ B+ AB+ O+ A- B- AB- O-
A+ Yes No Yes No No No No No
B+ No Yes Yes No No No No No
AB+ No No Yes No No No No No
O+ Yes Yes Yes Yes No No No No
A- Yes No Yes No Yes No Yes No
B- No Yes Yes No No Yes Yes No
AB- No No Yes No No No Yes No
O- Yes Yes Yes Yes Yes Yes Yes Yes

Universal Donor

In the event of an emergency when it is not possible to cross-match, O Rh. Negative blood may be given to the patient. O Rh. Negative is also termed as Universal Donor.

In layman’s terms, O Rh Negative can be termed as that blood which has no Antigen – neither ‘A’ nor ‘B’ nor ‘Rh’. In other words, this blood group has nothing which is foreign to the recipient.

Universal Recepient

Similarly, AB Rh Positive is termed as a Universal Recepient. He/she can receive blood from anybody.

In layman’s terms, AB Rh Positive can be termed as that blood which has all the Antigens – ‘A’, ‘B’ and ‘Rh’. Therefore there is nothing foreign for the persons having this blood group. They can receive blood from anybody.

Theoretically, Rh Negative can be given to Rh positive of the same A,B,O, group.