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Blood Group Testing: What you need to know


A blood group is a way to categorize the type of blood a person has. Our blood differs from person to person, based on the presence (or absence) of certain molecules on the surface of red blood cells. These substances, usually protein in nature, are called antigens. There are a large number of blood group systems, although we’ll concentrate on two of the well-known systems in this article.

What are common blood groups?

An individual’s blood group is determined by the presence of components (called antigens) on the surface of their red blood cells. Conversely, an antibody is present in the plasma, the fluid component of blood. The most important blood group system is the ABO followed by Rh. There is a great variety of other blood group systems, if you need to learn more see the reference below.
The table below summarises the ABO blood groups as determined by the presence of red cell A or B antigen.

Red Blood cell AntigenAntibody in plasmaBlood Group

Its important to note the ABO system is further subdivided into smaller subgroups. For example, group A has A1 and A2 subgroups

The second most important blood group system is the Rh system. This blood group is determined by the presence or absence of D antigen on the red blood cell. When present, it’s designated as Rh+ and Rh- when absent.
The ABO and Rh systems are usually tested and reported together. So, blood group, A person will be designated group A+ when Rh antigen is present and A- when it’s absent. The same applies to B, AB, and O blood groups.

What Determines Blood Group

The type of blood group a person has is determined by inheritance. Both the mother and father contribute genes that eventually determine the child’s blood group.

Blood Grouping and Cross-Matching

Blood group testing is usually carried out by the blood transfusion unit (BTU, blood bank) or within the hematology section of a medical laboratory. To find out someone’s blood group, the procedure is outlined below


Patient blood is mixed with various antisera (see image on the right). After mixing, agglutination/clot formation is checked. The well with agglutination indicates the presence of a particular antigen


This refers to the mixing of a drop of blood of the recipient with a compatible donor ( i.e. same ABO Rh group) to check for agglutination. This step ensures the blood does not contain other less frequent antigens that may cause incompatibility in the recipient.

Blood Group Antisera

Indications: Why and when blood grouping is done

There are a number of scenarios that require an individual to have their blood group test tested. These include:

  1. New mothers attending ANC for the first time. Checking a mother’s blood is a part of the AnteNatal Care Profile panel that you can read more about here.
  2. Newborns – In some countries, babies are blood typed immediately after birth.
  3. Blood donation and transfusion. During blood donation, the donor must have their blood group checked. Conversely, a recipient of blood or blood products must have their blood group known for them to ensure they receive compatible blood.
  4. Persons undergoing surgery. As part of pre-operative preparation, the patient’s blood group should be known in case an emergency transfusion is required during surgery.
  5. Travel – some countries require travelers’ blood group
  6. Joining college, military training, or other select jobs eg emergency services, etc.
  7. Any person who wants to know their blood group.

Final Words

Blood grouping is an important test done to determine someone’s blood group. It’s prudent for everyone to know their blood group.

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