Harr Immunology, Serology & Blood Bank (ISBB) Practice Test

In the Rh blood group system, individuals are classified based on the presence or absence of specific antigens on the surface of red blood cells. The Rh system is primarily identified by the D antigen, which is the most clinically significant antigen in this group.

An individual who possesses only the D antigen is classified as Rh positive. This is because the presence of the D antigen denotes a positive status in the Rh classification. Essentially, the identification of an individual as Rh positive is determined by the presence of the D antigen, and any other variations or combinations involving the D antigen that are present would not change their Rh classification to negative.

In contrast, Rh negative individuals lack the D antigen entirely. Rhnull refers to a rare phenotype where all Rh antigens are absent, and total Rh is not a standard classification used in blood typing. Therefore, only the presence of the D antigen within the Rh system directly leads to the classification of an individual as Rh positive.