Blood grouping and Rh typing

What is Blood Grouping?
Blood group testing is done to determine a person’s blood group (A, B, AB, or O) and Rh type. The blood group of a person is predicted by the presence of a specific antigen marker on the surface of the red blood cells (RBCs). When antigen A is present, the person has A blood group, B antigen is present in the B blood group. Consequently, both antigens A and B are present in AB, and no antigen in the O blood group.

The test also determines the Rh (Rhesus) factor. People who have Rh antigen on their RBCs are Rh+ (positive), while those who do not are Rh- (negative). This test is necessary for safe blood transfusions and to determine the risk of Rh factor incompatibility during pregnancy.

Why is Blood Grouping done?

• To determine compatibility with donated blood before receiving a transfusion of blood or blood components
• At the time of donating blood, tissue, organ, or bone marrow or getting registered as a potential donor
• To determine the risk of Rh factor incompatibility between the mother and fetus before pregnancy or during pregnancy

What does Blood Grouping Measure?

The blood grouping test is done to identify blood group of a person. The blood group of a person is denoted on the basis of certain specific antigen markers present on the surface of the red blood cells. These marker antigens are glycoproteins and help the body to recognize its own type of RBCs. According to ABO and Rh blood group systems, three types of antigen markers are commonly found on RBCs, namely A, B, and Rh, and the presence or absence of these antigen markers determine the blood type of a person. Thus, a person with antigen A belongs to blood group A, one with antigen B belongs to blood group B, those with both antigens A and B belong to group AB, while those without either antigen A or B belong to group O. Also, people who have Rh antigen on their RBCs are Rh+ (positive), while those who do not are Rh- (negative).

Antibodies are naturally created by the body against incompatible blood antigens. People with blood group A have anti-B antibodies against type B antigens and those with blood group B have anti-A antibodies against type A antigens. People with blood group AB do not have any of these antibodies, while those with blood group O have both anti-A and anti-B antibodies. Rh antibodies are produced by people of Rh-blood group upon exposure to Rh antigens in Rh+ blood type. Blood transfusion between incompatible blood types causes an antigen-antibody reaction which causes the RBCs to clump together and be destroyed. Hence blood groups of donor and recipient must match to ensure the success of the blood transfusion or organ transplant.

The antigen-antibody reaction between incompatible blood types forms the basis of the Blood Typing Test. The collected specimen is treated with collected or synthetic A, B, and Rh antibodies and observed for agglutination (clumping). If agglutination (clumping) of RBCs is seen upon treatment with anti-A antibodies, the sample is of blood type A. If agglutination is seen upon treatment with anti-B antibodies, the sample is of blood type B. If agglutination does not occur upon treatment with either anti-A or anti-B antibodies, the sample is of blood group O, and if agglutination occurs with both these antibodies, the sample is of blood group AB. The occurrence of agglutination upon treatment with Rh antibodies indicates Rh+ blood type, while no agglutination indicates Rh- blood type.