Rh factor is a:
**Core Concept**
The Rh factor is a specific antigen present on the surface of red blood cells (RBCs) in most individuals. It is a crucial determinant in the ABO blood group system, which is used to classify blood types based on the presence or absence of specific antigens on RBCs.
**Why the Correct Answer is Right**
The Rh factor is a protein (more specifically, a glycoprotein) that is encoded by the RHD gene. It is expressed on the surface of RBCs and can trigger an immune response if an individual with Rh-negative blood receives Rh-positive blood. This is because the Rh factor is recognized as foreign by the immune system, leading to the production of antibodies against it. The Rh factor plays a critical role in transfusion medicine, as Rh incompatibility between the mother and fetus can lead to hemolytic disease of the newborn.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a valid description of the Rh factor.
**Option B:** While the Rh factor is an antigen, it is not a type of antibody.
**Option C:** The Rh factor is not a type of blood cell; it is an antigen present on RBCs.
**Clinical Pearl / High-Yield Fact**
In the context of blood transfusions, Rh incompatibility between the mother and fetus can lead to hemolytic disease of the newborn, which can be life-threatening if not managed promptly.
**Correct Answer:** C.