Final answer:
The Rh antigen crucial for transfusion reactions is the Rh D antigen. Compatibility is essential to avoid reactions, and Rh-negative individuals can form antibodies against Rh-positive blood.
Step-by-step explanation:
The Rh antigen of importance to transfusion reactions is the Rh D antigen. This antigen is the most immunogenic and clinically significant of the Rh blood group system. Individuals who have the Rh D antigen on their erythrocytes are described as Rh positive (Rh+), and those who do not are Rh negative (Rh-). During blood transfusions, it's critical that Rh compatibility is considered to prevent transfusion reactions. People who are Rh negative can develop anti-Rh antibodies upon exposure to Rh-positive blood, with risks such as hemolytic disease of the newborn (HDN) in subsequent pregnancies; this is preventable with treatments like RhoGAM.