How is blood group determined?

How are blood groups determined?

A blood type (also called a blood group) is a classification of blood based on the presence or absence of a variety of antigens on the surface of red blood cells (RBCs).

The most important of which are the A, B and O antigens. People are divided into four major blood types: A, B, AB and O, depending on which antigens they have.

 

The type of antigen one has tells us what the blood type is. For example, if someone has ‘A’ antigens on his/ her blood cells, that person’s blood type is ‘A’. If someone has both A and B antigens, they are type AB. And if someone has no antigens, that person’s blood type is O.

Every individual inherits one antigen from each of their parents and is determined by two factors: the ABO grouping system and the Rh (i.e. rhesus) factor. They determine someone's blood type (A, B, AB and O, with + and - denoting Rh status).

(The Rhesus factor, also known as the Rh factor, is an antigen that exists on the surface of red blood cells in most people. People who have the Rhesus factor are considered to have a "positive" (+) blood type, such as A+ or B+. Those who don't are considered to have a "negative" (-) blood type, such as "O-" or "AB-." The Rhesus factor gets its name from experiments conducted in 1937 by scientists Karl Landsteiner and Alexander S. Weiner. Their experiments involved rabbits which, when injected with the monkeys red blood cells, produced an antigen that is present in the red blood cells of many humans.)

The A and B antigens are called the 'dominant' ones. This means that if a person has one B and one O antigen the B will be dominant over the O and their blood reacts as type B.


For each antigen on the blood cell, the opposite antibody is produced in the plasma. For example, type B blood has anti-type A antibodies.

To determine somebody’s blood group, a medical kit is used, which consists of a sterilized needle and a test card. Finger of the person whose blood group is to be determines is pricked with the sterilized needle and drops of blood are taken. These blood drops are then spread on each fields of the test card. It is thoroughly mixed until there appear marks on the test card.

The fields on the test card contains antibodies, which will provoke a reaction with antigens on the red blood cells. Marks formed due to this reaction will give us the type of blood

  • If the blood type is A, a mark will appear in the field: anti-A.
  • If the blood type is B, a mark will appear in the field: anti-B.
  • If the blood type is AB, a mark will appear in the fields: anti-A, anti-B.
  • If the blood type is O, no mark will appear on the test card.

 

This is how a blood group is determined.

There is another method which helps you in determining your blood group. But for this you need to know your parents blood groups. Here are the possible blood group combinations and the type they produce:

  • O parent x O parent = O child
  • O parent x A parent = A or O child
  • O parent x B parent = B or O child                                                                                            
  • O parent x AB parent = A or B child
  • A parent x A parent = A or O child
  • A parent x B parent = A, B, AB or O child
  • A parent x AB parent = A, B or AB child
  • B parent x B parent = B or O child
  • B parent x AB parent = A, B or AB child
  • AB parent x AB parent = A, B or AB child

 

 

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