For the ABO grouping, the antibodies produced against the antigens A and B are termed antibodies a and b respectively. Normally, in order not to cause any reaction; if you are of blood group A,
your body produces antibodies b, if you are of blood group B, your body produces antibodies a, if you are of blood group AB, your body produces neither of the antibodies and if you are of blood group O, your body produces both antibodies. For the Rh grouping, the antibodies produced against the D antigen are termed antibodies d. Normally, in order not to cause any reaction; if you are D positive, your body doesn’t produce any d antibodies.
To understand the importance of proper matching of blood before transfusion, let us pick a classical example:
Just at the ABO grouping level, supposing you are of blood group A, you will have already produced antibodies b in your blood. In the event where a blood type B is introduced into your system, the antibodies b in your system will react against the introduced type B red blood cells causing massive hemolysis (breakdown of red blood cells). The subsequent effects can be very endangering to you, even to death.
Going down to the Rh grouping level, supposing you are of blood group “A Negative”, the D antigen is foreign to your body system since you don’t have it. In the event where a blood type “A positive” is introduced into your system, even though the A antigens match such that the already produced b antibodies cannot react with the introduced A antigens, the introduced “foreign” D antigens will stimulate your immune system to produce antibodies d against the D antigens. This results in a relatively lesser hemolysis (red blood cell destruction) in first transfusion but similar level hemolysis in subsequent transfusion of same blood type (when compared to the ABO grouping mismatch transfusion). Contrarily, when an “A Negative” blood is introduced into an “A Positive” patient, there is no serious reaction aftermath because, the already produced b antibodies do not react with the introduced A antigens, there are no already produced d antibodies, and there are no introduced D antigens to stimulate the production of d antibodies, hence no reaction. (Yet, this type of transfusion is only allowed in emergencies).
The endangering effect is true for all other mismatched blood group transfusions. It is therefore a prerequisite that blood to be transfused matches exactly that of the recipient. The only exception is when considering “O Negative” donors and “AB Positive” recipients. When an “O Negative” blood is introduced into a patient of any of the blood groups, whatever antibodies present in the patient don’t get any antigens to react to because “O Negative” blood lacks A, B and D antigens. Much the same way, when an “AB Positive” patient receives blood from any of the blood groups, there is no reaction to any of the antigens because the patient lacks antibodies a, b and d. For the above reasons, people of “O Negative” blood group are referred to as “Universal Donors” and those of “AB Positive” blood group are referred to as “Universal Recipients”.
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This article was written by Joseph Ofori and reviewed by Arnold Agyemang, who are both professional medical laboartory scientists.