What indicates the presence of the Rh D antigen?

The presence of the Rh D antigen is indicated when the antigen itself is present on the surface of the red blood cells. The Rh D antigen is a specific protein that determines whether a person's blood type is positive or negative in relation to the Rh factor. In this case, the correct answer reflects that the antigen is present, which is the defining characteristic of Rh-positive blood types, such as A+, B+, AB+, and O+.

When blood is type A+, it means that there is both A antigen and the Rh D antigen on the red blood cells. This is why blood types can be classified as positive; it indicates the presence of the Rh D antigen. Therefore, acknowledging that the antigen is present directly correlates to distinguishing between Rh-positive and Rh-negative blood types, thereby affirming the correct choice.

Recognizing that the Rh D antigen is indicative of positive blood types provides critical information in prenatal care and blood transfusions, as mismatched Rh factors can lead to serious complications for both mothers and infants.