Due to the recent campaigns for blood donors, people have become interested in what type of blood they have—group A or B, Rh-(positive) or Rh-(negative). What does it mean to be of group A or B and why cannot one type of blood be mixed with another?
In order to understand the significance of blood classification, it is necessary to first understand a few simple facts about how blood reacts to various substances with which it comes into contact. If a foreign substance is introduced into the blood stream the blood cells produce a substance which will counteract this foreign substance. For the sake of convenience the foreign substance, whatever it may be, is called an antigen, that substance which is produced by the blood and which serves to eliminate the foreign substance is called an antibody, and the reaction of the one upon the other is called an antigen antibody reaction. Every type of foreign matter which finds its way into the blood stream stimulates a certain antibody to be produced. For example, if the antigen or foreign substance is a poison or toxin the antibody produced is called antitoxin and the reaction in which the antibody removes the antigen is a toxin-antitoxin reaction. If the antigen consists of the cells of a plant or animal, the antibody can be of two types—lysin or agglutinin depending on the type of cell. Lysin splits the foreign cells and makes it easier for the white corpuscles in our blood to eliminate the cells. Agglutinin causes the foreign cells to clump together and thus makes it easier for the white corpuscles to attack them. All these antibodies which are produced in the blood when a foreign substance is introduced and make the person immune or free him from the effects of the foreign matter are called immune antibodies. In addition to these immune antibodies there are antibodies which naturally occur in the blood and there are called normal antibodies.
In 1900 Dr. Karl Landstiener in Vienna experimented with human blood. He noticed by means of the microscope that when he mixed a drop of blood from one person with a drop of blood from another person that agglutination, a clumping together of the cells of blood, sometimes occurred. This clumping did not always occur but only when the blood cells of certain people were mixed with those of other people. He concluded that there are normal antigens and antibodies in the human blood which caused this phenomena. Further investigation of his discoveries verified his findings and further discovered that there are two such normally occurring antigens in the human blood. For sake of convenience these antigens were called A and B.
It was found that a person could have either antigen A or B, both A and B, or neither A nor B. Thus a person who was of blood type A would have antigen A, type B antigen B, type AB antigen A and B, type O neither antigen A nor B. One can see now that if a person were of group A and had antigen A he could not have the corresponding antibody A in his blood stream because his blood would clump together and he would not be able to live. However, a person who has antigen A would have the antibodies of the other blood groups in his blood. Thus the person of group A would have antibody B in his blood and if his blood were given to a person of group B the blood cells would clump together causing the circulation of the person of group B to be hindered and finally cause death.
Many other types of normal antigens have been discovered in the human blood. In 1927 the M and N antigens were discovered. More recent than that, the Rh and Hr antigens were found, and people are further classified into Rh (positive) and Rh (negative).
From the foregoing discussion one can plainly see that it is very important that a person’s blood be classified before he receives a transfusion. This classification must be very accurate because one mistake could cause the death of the person receiving the transfusion.