Facts about the D antigen and antibody:
- Part of the Rh antigen group, a highly immunogenic and complex group comprised of 49 antigens.
- For RhD-negative people, there is an approximately 50% chance of immunization after each exposure to D antigens.
- The Rh group is second in importance to the ABO group.
- Anti-D is a primary concern in obstetrics as the main cause of HDFN. Rh-negative patients who have been determined to not have an Anti-D are recommended to receive Rh Immune Globulin (RhIG) in order to prevent an Anti-D from forming.
- Antibodies to the system are primarily IgG and are capable of causing significant hemolytic transfusion reactions.
- D Antigen is found in 85% of Caucasians, 92% of African Americans, and 99% of Asians.
- D Antigen is routinely screened for in patients having a blood type performed.
- The D antigen is actually a mosaic of different epitopes and can also exist as Weak D or Partial D.
- Weak D phenotype is a quantitative polymorphism where all D epitopes are present but have a reduced expression. Weak D typically requires an indirect antiglobulin test (IAT) to detect. Anti-D is typically not produced if exposed to RhD antigens. Transfusion recommendations vary for Weak D positive patients. Follow your institution's policies for transfusion.
- Partial D is an expression of some, but not all, RhD epitopes. Partial D is detected by most commercial Anti-D antisera, and Anti-D can form after exposure to D antigens.
- Molecular testing is recommended for anyone typing as D+ with commercial antisera and producing an Anti-D to determine if they are Partial D producing an alloantibody or full RhD+ producing an autoantibody. An allogeneic Anti-D has severe clinical implications whereas an autologous Anti-D typically does not.
- There is no antithetical d antigen.
Table 5. D Facts.| Ag/Ab | Ag Frequency (White) | Ag Frequency (Black) | Dosage | Enzyme Interaction | Antibody Class | Complement Binding | Clinically Significant |
| D | 85% | 92% | Yes | Enhanced by | IgG | No | Yes |
