Unit II

Author: Dr Pramila Singh

2.4 The Rh Blood Group System, Antigen, and antibody involved.

Rh blood group system is named after the Rhesus monkey. The red blood cell surface of Rhesus monkey has a special antigen. This antigen is named as Rh factor. Rh factor is also present in the red blood cells of the human body. In India, Rh factor is found in 93% of the population. On the basis of the Rh factor, human blood is divided into two groups. Human blood containing Rh factor in red blood cells is the Rh+ve (positive) blood group. Human blood without Rh factor in red blood cells is called the Rh-ve (Negative) blood group.

Significance of Rh blood group system: Rh blood group system is considered during blood transfusion and pregnancy.

1. Blood transfusion: Individuals with the Rh+ Blood group can receive blood from both the Rh+ blood group and Rh – blood group. But the Rh- blood group can receive blood only from the -Rh blood group.

   Reason: Rh+ blood has Rh factor (Rh antigen). The Rh-blood recognizes the Rh antigen of Rh+ blood and will produce Rh antibody. Rh antibody will interact with the Rh antigen of Rh+ blood. This interaction will cause red blood cell hemolysis. This may be fatal in nature.

2. Pregnancy: Rh blood group system becomes very crucial in pregnancy. Rh –ve blood group mother pregnant with Rh+ fetus will be fatal and will develop complications.

   Reason: Foetus blood enters the mother’s blood circulation. Mother’s blood recognizes fetus's Rh+ blood antigen and develops Rh antibody. This is called Rh sensitization. There will be a complication and Red blood cell hemolysis. But it is manageable. But in subsequent pregnancy with the Rh+ fetus number of Rh antibodies will increase in the mother’s blood. This will destroy the fetus's red blood cells. There will be serious complications such as anemia and jaundice in the infant (newborn baby).

3. Mother blood has Rh antibody and fetus blood has Rh antigen. The Rh antibody of the mother's blood will interact with the Rh antigen of the fetus.

Antigen involved in Rh blood group system

Rh factor is a protein present on the red blood cells surface of the Rh+ blood group. This Rh factor acts as an antigen. Rh-blood has no Rh factor in its red blood cells. Thus, the Rh antigen is present in red blood cells of Rh+ blood and absent in the red blood cells of Rh- blood.

There are three types of Rh antigen. These are Rh antigen C, Rh antigen D, Rh antigen E. Three genes c, d, and e develop these antigens. Gene c develops antigen C, gene d develops antigen and gene e develops antigen E. Rh antigen D (Rh D) is the main and strongest antigen present on the surface of red blood cells surface. Rh D antigen (Rh factor) is highly immunogenic. Rest Rh antigens are very weak antigens and clinically not significant.

Entry of Rh factor of Rh+ blood into Rh-blood stimulates the immune system of the Rh-ve blood group. This produces Rh antibodies in Rh-blood, especially Anti D antibodies. Anti-D antibody destroys Rh+ red blood cells. It is significant during blood transfusions and pregnancy.

Blood transfusion: Entry of Rh+ blood to Rh- blood during blood transfusion creates a problem. The Body of the Rh-individual recognizes Rh+ blood and produces Anti D antibody. Anti-D antibodies attack RBCs of Rh+ blood and destroy them. This causes serious complications.

Pregnancy: Rh- mother carrying Rh+ fetus creates serious complications. The immune system of Rh- mother will produce Anti D antibody. Anti-D antibodies will attack the fetus's red blood cells. It is called Rh sensitization. In the first pregnancy, there will be controllable complications. But in a second pregnancy with Rh+ fetus will produce serious complications.

Antibody involved in Rh blood group system

The antibody involved in the Rh blood group system is called the Rh-D antibody. Rh D antibody is not a naturally occurring antibody in the blood. It is produced by the Rh-blood group immune system when it comes in contact with Rh+ blood during a blood transfusion or during pregnancy. Rh D antigen is of IgG type antibody.

During pregnancy, it is developed if the mother is Rh- and the fetus is Rh+. First contact causes Rh sensitization. Subsequent contact during transfusion or pregnancy will cause hemolysis of Rh+ red blood cells.

2.5 Principle and procedure of Rh grouping

Principle: The principle of the Rh blood group system is based on the presence or absence of Rh antigen in the red blood cells, surface. Rh antigen is also called Rh D antigen (Rh factor). Rh blood group system classifies human blood into two groups. These are the Rh+ blood group and Rh- blood group. This classification is based presence or absence of Rh antigen (Rh D antigen or Rh factor) on red blood cells of the blood. The Rh+ blood group has Rh antigen in its red blood cells of blood. Rh- blood group does not have Rh antigen in its red blood cells of blood.

To detect the Rh blood group, an individual’s blood sample is mixed with the Anti-D antibody. If individual’ red blood cells carry Rh antigen then Anti D antibody will combine with Rh antigen. There will be agglutination in the sample. It will confirm Rh+ blood. If individual’ red blood cells do not carry Rh antigen then there will be no agglutination in the sample. It will confirm Rh- blood.

Procedure: There are two methods to detect the Rh blood group. These are the forward grouping method and reverse grouping method. The forward grouping method is most commonly used. It is also called direct agglutination test or slide agglutination test. The following steps are followed to detect the Rh blood group by direct agglutination test.

1. Collection of blood samples: Collect blood samples. Use EDTA anticoagulant to prevent blood clotting.

2. Preparation of reagent: Use Anti D antibody available in the laboratory.

3. Mixing of blood sample with Anti D antibody: Place a drop of blood sample on a sterile glass slide. Add a drop of Anti D antibody reagent to the drop of the blood sample. Mix blood sample and Anti-D antibody.

4. Observation of agglutination: Rotate or rock slide gently to allow a reaction between blood and Ant D antibody. If agglutination occurs, it indicates Rh+ blood. If agglutination does not occur, it indicates Rh-blood.

The result can be confirmed by using the reverse grouping method. It is performed by mixing an individual’s blood plasma with known Rh+ red blood cells. If agglutination occurs, it will confirm the Rh+ blood group. If agglutination does not occur, it will confirm Rh- blood group.

Dr Pramila Singh