Rh Blood Group

The Rhesus or Rh antigen is a class of agglutinogen on the red blood cells or RBCs. Its presence or absence categorizes a person as Rh-positive or Rh-negative.

When reporting a person's blood group, the Rh antigen is typically combined with the A and B antigens.

For instance, the blood type of a person with antigens A and Rh is designated as A-positive. Conversely, in the absence of Rh antigen, the person's blood is referred to as A-negative.

Unlike the ABO system, the plasma does not naturally contain anti-Rh antibodies.

So, exposure to the Rh antigen can trigger an immune response in Rh-negative individuals, leading to hemolysis.

For example, suppose an Rh-negative mother carries an Rh-positive fetus. In that case, the mother's immune system recognizes the Rh antigen on the fetal RBCs as foreign, triggering the production of anti-Rh antibodies.

Typically, these antibodies do not interfere in the first pregnancy. However, in subsequent pregnancies with Rh-positive fetuses, the fetal RBCs are at risk of hemolysis due to the existing anti-Rh antibodies in the mother's blood.