The blood group or blood type is a classification of the blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glucolipids depending on the blood group system.
The RBC cell membrane contains 2 main classes of antigens, namely 1) ABO and 2) Rh system.
1) The ABO system is the most important blood group system. The cell membrane of RBC contains antigen called agglutinogens. There are 2 such agglutinogens, A and B and so blood in human beings can be classified into 4 groups based on this.
i. Persons whose RBC membrane contains A agglutinogen in their blood can be categorized as group A.
ii. Similarly persons whose RBC membrane contains B agglutinogen in their blood can be called group B.
iii. Some persons have both A and B agglutinogens in their blood and therefore called AB group.
iv. Some persons have no agglutinogen in their RBC membrane and so is named as O blood group.
The plasma (fluid) in the blood also contains agglutinins which are antibodies present in the blood. There are 2 main classes of antibodies in the blood called 1) anti A antibody or alpha antibody, and 2) anti B antibody or beta antibody. Based on the agglutinins present in the human plasma the blood can be classified into 4 groups.
i. Persons whose blood plasma contains anti A antibody or alpha antibody.
i. Persons whose blood plasma contains anti B antibody or beta antibody.
iii. Persons whose blood plasma contains both anti A antibody and anti B antibody.
iv. Persons whose blood plasma contains no antibodies.
Blood Groups:
When group A blood is admised with the serum or plasma containing A agglutinin and the RBC containing A agglutinogen, the anti A agglutinin attacks the A agglutinogen and the blood gets agglutinated or the RBCs are clumped together. The clumped RBCs can cause 1) blocking the circulation in a small blood vessel or arteriole producing disaster and 2) undergo hemolysis and produce hazards including free Hb blocking renal tubules causing jaundice.
A person whose blood group is A, cannot have anti A agglutinin in his or her blood. Also in a person with B group, there can be no anti B agglutinin in his or her blood. Likewise in a person whose blood group is AB group there cannot be any agglutinin either A or B present in his or her plasma, and in a person whose blood group is O group there will be both A and B agglutinin present in his or her plasma.
For example, group A blood is transfused in a person belonging to group B,
Donor's blood contains A agglutinogen in the RBC and beta agglutinin in the plasma, while the recipeint's blood contains B agglutinogen in the RBC and alpha agglutinin in the plasma. The donor's RBC will be clumped and lysed by the recipient's alpha agglutinin. However the beta agglutinin of the donor will be so much diluted in the recipients blood that it will cause no harm of the recipient's RBCs.
So in a mismatched blood transfusion, donor's RBCs are lysed but the recipients RBCs remain unharmed.
O group of blood can be transfused (donated) to all groups of the ABO system, so it is called as the universal donor. AB group of blood is called the universal recipient because any of the blood groups can be safely transfused (received) in the AB group person All these groupings are safe provided there is no Rh incompatibility.
a) Individuals with type A blood can receive blood from donors of type A and type O blood.
b) Individuals with type B blood can receive blood from donors of type B and type O blood.
c) Individuals with type AB blood can receive blood from donors of type A, type B, type AB, or type O blood. Type AB blood is called the universal recipient.
d) Individuals with type O blood can receive blood from donors of only type O.
e) Individuals of type A, B, AB and O blood can receive blood from donors of type O blood. Type O blood is called the universal donor.
RBC Compatibility Diagram
Plasma Compatibility Diagram
2) Rh System:
Rh owes the name to the rhesus monkey in whom this group was first discovered. There are several Rh groups but only factor D is clinically important. When Rh D is present in the RBC, the person is said to be
Rh +ve and when Rh is absent in the RBC, the person is Rh -ve. About 90% of the population is Rh +ve and about 10% is Rh -ve. Rh -ve persons provided they have not received an Rh +ve blood group have no Rh antibodies.
In ABO system agglutinins or antibodies occur naturally, that is without being exposed to the corresponding antigen. In Rh system, Rh antibodies are not naturally occurring and it appears only when Rh +ve RBC's enter in a Rh -ve person's blood. The exposure clinically occurs under 2 instances, i) when a Rh -ve person recieves Rh +ve blood through transfusion and ii) when Rh -ve mother conceives a Rh +ve fetus.
An Rh D-negative patient who does not have any anti-D antibodies (never being previously sensitized to D-positive RBCs) can receive a transfusion of D-positive blood once, but this would cause sensitization to the D antigen, and a female patient would become at risk for hemolytic disease of the newborn. If a D-negative patient has developed anti-D antibodies, a subsequent exposure to D-positive blood would lead to a potentially dangerous transfusion reaction. Rh D-positive blood should never be given to D-negative women of child bearing age or to patients with D antibodies.
There are the main blood groupings which we have to consider when doing a blood transfusion. Hope you will keep these in mind when you come across blood any transfusion procedure in the future.
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