Human blood group is classified into two major blood groups system across the world. Its ABO Blood group system and Rh Blood group system. In ABO blood group system, Human blood is classified as A, B, AB or O blood group. Rh blood group system can have Rh +ve or Rh -ve.
ABO Blood Group
Blood groups are classified depending on the presence of antigen on the blood cells. If a person’s red blood cells express the presence of A antigen, then his blood group is said to be of blood group A and if person’s red blood cells express the presence of B antigen on the surfaces of blood cells then he or she is said to be of blood type B. People with red blood cells which do not express A antigen and B antigen then he or she is said to be of blood type O.
Genetic inheritance will determine the blood group of the child. When a child inherits a pair of A-genes from its parents which has the capacity to express A antigens on red blood cells surface. Such child will have blood group A.
When a child inherits the pair of B genes which is capable of coding the presence of B antigens on the red blood cell’s surface, then such child will have blood group B.
When the child inherits A antigen from father and B antigen from its mother, such child is said to have blood group AB.
When child neither inherits A gene nor B gene, then it won’t be able to express Antigens A and B, which will make them recessive and it belongs to blood group O.
When the child inherits one A or B gene along with one O gene results in either an A or a B, but not to an O blood type.
There are many other rare blood groups such as Bombay Blood Group, INRA, Duffy-negative blood and many other. ABO blood group is incompatible with these rare blood groups.
Blood group is said to be of Rh +ve or Rh -ve depends on the presence or absence of rhesus factor. Presence of rhesus factor makes a blood group Rh +ve and absence of rhesus factor will make blood group as Rh -ve. The blood transfusion will be carried out depending on the ABO blood group and RH blood group compatibility. We divide blood groups as A+ve, A-ve, B+ve, B-ve, AB+ve, AB-ve, O+ve and O-ve.
A1+ve and A2+ve Blood Group
Blood groups are determined by the presence of the type of antigen the surface of the red blood cells. There are many blood antigens present. A – antigen, B – antigen are common.
Some of the other blood antigens that are used in blood typing are C factor, D factor, E factor, S factor, M factor, K factor, Le(a) Factor, Fy(a) Factor, Fy(b) factor and Jk(b) Factor are to name few.
Presence of antigens helps in deciding the blood group of the person. Bombay blood group people will not have A and B antigen, which makes lab technician think that this falls under blood type O. But, Bombay Blood group people will not have even H antigen which is present in O blood type people.
Like that, A blood group people will have the presence of A Antigen. Means, the surface of red blood cells of such person will have A antigen. But, within A antigen there are more than 20 different subtypes.
When a person’s A genes are able to code for expressing A1 subtype antigen then he is said to have A1 blood group. If a person’s A gene is able to code for another subtype antigen called A2 antigen, then he is said to have the A2 blood type. Presence or Absence of Rh factor makes them either Rh+ve or Rh-ve.
So a person who has A1+ve will have the A1 subtype of an A antigen and a person who has A2+ve will have the A2 subtype of an A antigen.
A1 and A2 subtypes are very common among 22+ subtypes of A antigen, other subtypes are very rare. 99% of people will have either A1 or A2. 80% of the people are said to have A1 subtype and it is very common.
When a person is said to have A1B that means he is able to code for Antigen A with subtype A1 and also antigen B. This makes his blood group as A1B. When a person is said to have A2B that means he is able to code for Antigen A with subtype A2 and also antigen B. This makes his blood group as A2B.
The A1 and A2 subtypes are so similar that they do not need to be distinguished for the purposes of transfusion.
Some of the other A subtypes are different enough to complications when blood is being typed, but these subtypes are so rare that such issues arise very infrequently.