Question

How does the blood typing test work? If provided with a hypothetical situation, be able to predict the results.

Answer 1

Blood typing test helps to identify the individual’s blood group.

There are four blood groups:

A – A⁺ and A^- - Contains antigen A and Rh antigen present or absent (A+ or A-)

B – B⁺ and B^- - Contains antigen B and Rh antigen present or absent (B+ or B-)

AB – AB⁺ and AB^- - Contains both antigens and Rh antigen present or absent (AB+ or AB-)

O – O⁺ and O^- - Does not contain any of the antigens and Rh antigen present or absent (O+ or O-)

ABO typing and Rh typing helps to predict the blood group.

Each blood group contains an antigen of same type, and Rh factor antigen (present or absent), these can be identified in blood typing test. For example blood group A contains antigen A on its RBC’s. If Rh factor antigen is present in blood, it is positive and if Rh factor is absent it is negative.

There are three steps in blood typing:

• Forward typing
• Reverse typing
• Rhesus typing

Forward typing: Individual’s blood is collected by using a needle and it is mixed with two different antibodies (Anti-A and Anti-B).           

• If the blood is reacted or agglutinated with Anti-A antibody, it indicates the blood group is A and
• If it reacts with Anti-B, the blood group is B.
• If it reacts with both anti-A and anti-B, it indicates the blood group is AB.
• If it does not react with any of these two, it indicates the blood group O.

Reverse typing:

To ensure the results of forward typing reverse typing is used. In this type serum or plasma is mixed with anti-A and anti-B solutions.

If serum is agglutinated with anti-A, it indicates the blood group B.

If serum is agglutinated with anti-B, it indicates the blood group A.

If serum is agglutinated with both anti-A and anti-B, it indicates the blood group O.

If serum is not agglutinated with both anti-A and anti-B, it indicates the blood group AB.

Rhesus Typing:

This is used to determine the presence of Rh factor.

Here blood is mixed with solution of Rh antibodies,

If the blood is agglutinated with this solution, it indicates blood group has Rh factor antigen, hence it is positive.

If the blood is not agglutinated with this solution, it indicates blood group doesn’t have Rh factor antigen, hence it is negative.

Hypothetical situations: While blood transfusions, pregnancies, blood typing is used.

For example while blood transfusions the blood group of donor should be detected. If the blood group of donor is not matched with acceptor (patient), it leads to reactions and clumping of patient’s blood. This inturn leads to several serious health conditions.

If donor blood is blood group AB (contains both A and B antigen) and the acceptor has blood group O (does not contain any of the antigen and can produce both antibody A and B), antibodies will be produced in acceptor’s blood and causes reactions.

If the donor is Rh-positive and acceptor is Rh-negative, then Rh antibodies will be produced in acceptor and reactions will starts.

In pregnancies, particularly performing rhesus typing test is necessary. Because if mother has Rh^-ve and child has Rh^+ve, mother’s blood produces antibodies for Rh antigen present in fetus blood. These antibodies travel across the placenta and reacts with Rh antigen of fetus blood. It may not cause serious condition in first pregnancy, but in subsequent pregnancies it leads to hemolytic disorder in newborn.