Blood Group Testing
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). ‘Antigen’ 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 system
generates ‘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.– 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?
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 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.
Materials Required
Toothpicks
Blood sample
Alcohol Swabs
Lancet
Clean glass slide
Sterile cotton balls
Biohazard disposal container
Monoclonal Antibodies (Anti-A, B, and D)
All these equipment will be readily available in a blood test tool kit.
Procedure
1. Take a clean glass slide and draw three circles on it.
2. Unpack the Monoclonal Antibodies (MAB) kit. In the first circle add Anti-A, to the second
circle add Anti-B and to the third circle add Anti-D with the help of a dropper.
3. Keep the slide aside safely without disturbing.
4. Now wipe the ring finger with the alcohol swabs and rub gently near the fingertip, where
the blood sample will be collected.
5. Prick the ring fingertip with the lancet and wipe off the first drop of the blood.
6. As blood starts oozing out, allow it to fall on the three circles of the glass slide by gently
pressing the fingertip.
7. Apply pressure on the site where it was pricked and to stop blood flow. Use the cotton ball
if required.
8. Mix the blood sample gently with the help of a toothpick and wait for a minute to observe
the result.
Results:
Observe the agglutination reaction and record the result.
