Alterations in D Antigen Expression

When routine testing of red cell samples is performed using commercially prepared anti-D reagents, positive reactivity is expected to be strong. However, in some instances this reactivity may be weaker or not observed at room temperature immediate spin. Testing through the immunoglobulin phase may be required in order to detect the D antigen. Historically these samples were referred to as D^u type. Based on the lack of production of anti-D^u it was determined that this was not a new antigen. In some cases, in fact, individuals identified as D^u produced anti-D. These individuals are now categorized into different phenotypes defined by the mechanism that brings about the alteration of the D antigen expression.