AEMCA Practice Exam

What characterizes the antigen presence in Rh positive blood?

1. Absence of any antigens

2. Presence of A antigen only

3. Presence of an antigen on red blood cells

4. Presence of B antigen only

The correct answer is: Presence of an antigen on red blood cells

The presence of an antigen on red blood cells is a defining characteristic of Rh positive blood. In individuals who are Rh positive, there is a specific protein, known as the D antigen, found on the surface of their red blood cells. This D antigen is part of the Rh blood group system, which also includes other antigens, but the D antigen is the most clinically significant when it comes to blood transfusions and pregnancy. Rh positive blood means that the individual has inherited the gene responsible for producing this D antigen, leading to the classification of their blood type as Rh positive. This is particularly important to note in contexts such as pregnancy or blood transfusions, where the presence or absence of the Rh factor can lead to serious immune reactions if incompatible blood types are mixed. The other options do not accurately represent the characteristics of Rh positive blood. For instance, the absence of any antigens would refer to a very different blood type, and the presence of only A or only B antigens suggests blood types that are not directly related to the Rh factor. Each blood type's classification relies on both the ABO system (A, B, AB, or O) and the Rh factor (positive or negative), making it critical to understand the role of the Rh antigen