Blood Types and Blood Group Testing
All of us bleed red – but of various types. It is common knowledge that blood can be classified into different blood groups; news scrolls and WhatsApp texts carry urgent requests for a particular type of blood and Facebook’s ‘blood donor’ feature caters to requests based on blood groups. Those of us who are a part of any social network that provides a conduit for blood to flow from person to person, know that the following blood groups (or types) exist: A, B, AB, and O. Also familiar to us, is the positive or negative sign that accompanies these basic blood types, further segregating them into eight groups. On what basis, then, are these divisions organised?
ABO Blood Types
The ABO grouping system is based on the type of antigens that live on the surface of the red blood cells (RBCs). If the word ‘antigen’ rings a rusty bell, we may recollect that these are protein molecules that stimulate an immune response from the white blood cells (WBCs) in the body. These need not necessarily be foreign bodies: our systemgenerates ‘autoantigens’ on its own as well. The type of autoantigens that our RBCs carry determines our blood group in the following manner:
- Blood group A has type A antigens (and type B antibodies)
- Blood group B has type B antigens (and type A antibodies)
- Blood group AB has type A as well as type B antigens (and no antibodies)
- Blood group O has no antigens at all (and both types of antibodies)
(Antibodies are also protein molecules launched by the body to counter the effect of antigens.)
Rh Blood Types
A further classification is possible based on the Rh (Rhesus) factor. Named after the Rhesus monkey that was mistakenly thought to have the same antigen, this protein – which is also an antigen – is found on the cell membrane of RBCs. The determination of the various types within the Rh factor itself is a complex science, but as far as blood groups are concerned, the classification is based, quite simply, on their presence or absence. Blood that lacks Rh antigens is Rh-negative, and the other kind is Rh-positive. Accordingly, a plus or a minus sign is attached to the ABO classification, giving rise to these types: A+, A-, B+, B-, AB+, AB-, O+, and O-.
What is the significance of blood typing?
The problem and the answer both lie in the antigens. Since these substances trigger immune responses from the body, it is of utmost importance to ensure compatibility before blood transfusions and donations are made. If, for instance, a person of blood group B receives blood of type A, the recipient’s body will label the A-type antigens as foreign bodies, and resist the transfusion. It is for this reason that group AB can receive blood from any type (since it contains and recognises both types of antigens) but group O can only take from type O. The same rule applies for the highly immunogenic Rh-factor as well. Rh-negative mothers who first had an Rh-positive baby might develop antibodies that may harm an Rh-positive baby during the second pregnancy, leading to severe anaemia. It is not surprising, therefore, that many documents – ranging from university applications to employee ID-cards ask for the blood group to be specified.
What is the testing procedure?
The same principle mentioned above is applied in the laboratory.
In the first step, known as forward typing, antibodies that attack type A and type B blood are introduced into the blood sample, and the reaction is observed. If the target blood cells group together, it means that the blood sample has reacted with the antibodies. For instance, anti-A antibodies induce agglutination (grouping or clumping) in type A blood.
The second step is called reverse typing, and is performed on the serum left behind after RBCs and WBCs are removed. Blood of a predetermined type (either A or B) is added and its behaviour in the serum is observed – and this should confirm the result of forward typing.
The Rh-factor test also follows a similar pattern. Antibodies to Rh are mixed with the blood sample, and if there is a clumping reaction, the blood is Rh-positive.
Preparation and Accessibility
No prior preparation is required for a blood group test, other than the extraction of a blood sample. Any diagnostic centre will have a laboratory equipped to perform the test on this sample, but it is always safer to consult an established and reliable organization. Apollo Diagnostics gives the assurance of accurate testing and quick, authentic results. Since a lot depends on this basic test, the earlier it is done, the better. Find your nearest Apollo Diagnostics centre here (will add hyperlink later).