Blood Group Basics:
The most important blood groups in transfusion are the ABO blood group system and the RhD blood group system.Blood groups are determined by a protein (antigen) on the surface of the red cell. So, the ABO system has A and B antigens and the RhD system has the D antigen.In all, there are 30 major blood group systems. This means a person may be A RhD positive, and at the same time Kell (Kell system) positive, M and N (MNS system) positive and Lea and Leb (Lewis system) positive.
The ABO blood group system:
If you have blood group A then you have got the A antigen on your red cells.Blood group B means you have the B antigen, while group O has neither, and group AB has both A and B antigens.The ABO system has associated anti-A and anti-B antibodies, antibodies being the body's natural defence against foreign antigens. These antibodies are found in the plasma.Blood group A has the A antigen. This group recognises the B antigen as foreign and can make anti-B antibodies.Similarly, blood group B has the B antigen and therefore recognises the A antigen as foreign and can make anti-A antibodies.Group AB has both the A antigen and the B antigen so this group makes no antibodies.Group O has neither A nor B antigen so this group can be given safely to any other group. This is why Group O donors are known as ‘universal donors’. Group O can make both anti-A and anti-B antibodies if exposed to these antigens.Giving someone blood from the wrong ABO group could be life-threatening.For instance, the anti-A antibodies in group B attack group A cells and vice versa. This is why group A blood must never be given to a group B person.
The RhD system:
Scientists sometimes study Rhesus monkeys to learn more about the human anatomy because there are certain similarities between the two species. While studying Rhesus monkeys, a certain blood protein was discovered. This protein is also present in the blood of some people. Other people, however, do not have the protein. The presence of the protein, or lack of it, is referred to as the Rh (for Rhesus) factor.If your blood does contain the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood is said to be Rh negative (Rh-).This Rh factor is connected to your blood type. For example, your blood may be AB+ which means that you have type AB blood with a positive Rh factor. Or, you might have O- blood which means that you have type O blood with a negative Rh factor.It is particularly important for expectant mothers to know their blood's Rh factor. Occasionally, a baby will inherit an Rh positive blood type from its father while the mother has an Rh negative blood type. The baby's life could be in great danger if the mother's Rh negative blood attacks the baby's Rh positive blood. If this happens, an exchange transfusion may save the baby's life. The baby's blood can be exchanged for new blood that matches the mother's.