To gain understanding of different blood types, it's best to get started with some basic facts:
What is the origin of blood typing? It was only in the early 1900s that Karl Landsteiner was able to classify blood into its four basic types. Before this time, blood transfusions, including transfer of blood from animals to humans, proved to have some disastrous results. As doctors began to gain more understanding that humans have different blood types, some of which were incompatible, blood transfusions became a safe and routine procedure.
What is a blood type? Blood type is a classification of blood based on the presence or absence of antigen substances on the surface of red blood cells. A type of antigen, called agglutinogens, can be grouped into two types: type A and type B. These two types have different properties. If the agglutinogen is absent on the surface of the red blood cell, that blood type is classified as type O.
What are the different blood types? Each person gets an A, B, or O gene from each of his parents. These two inherited genes, when combined, determine your blood type. A and B are co-dominant, while O is recessive. Let us take a look at some scenarios:
a. A and O = blood type A
b. B and O = blood type B
c. A and B = blood type AB
d. O and O = blood type O
Apart from this basic ABO blood system, the Rhesus (Rh) system is another significant blood groups system. There are 5 main Rhesus antigens (C, c, D, E, and e) on the surface of the red blood cells, but RhD is the most important factor in blood typing.
The presence or absence of the RhD antigen is part of the blood type system: a positive (+) sign is affixed to the ABO blood type if RhD is present, and a negative (-) sign if RhD is absent. Each person also inherits positive or negative RhD from both his parents. Let us look at some scenarios:
a. + and + = + RhD
b. + and - = + RhD
c. - and - = - RhD
So for example, if a person has a B blood type and is positive for the RhD antigen, then his blood type is B+.
The most common blood type is O+, closely followed by A+. The rarest blood types are AB -, followed by B - and AB +.
What are the practical applications of blood typing? Blood types, though seemingly basic, are in fact very important in the field of medicine. During blood transfusions, for example, all precautions must be undertaken to make sure that the donor will receive only blood compatible to his blood type. In case incompatible blood is used, antibodies will attack the foreign RBCs and blood components, thereby producing several adverse effects including renal failure, shock or even death.
Blood compatibility is summarized as follows:
Blood type A = compatible with blood types A and O
Blood type B = compatible with blood types B and O
Blood type AB = compatible with blood types A, B, AB, and O
Blood type O = compatible with blood type O
To summarize, AB is called the universal recipient, while O is the universal donor.
These are just some facts to help you get started on your research. Good luck!