D Antigen
Definition
The most immunogenic Rh antigen, encoded by the RHD gene. Its presence defines Rh-positive; its absence defines Rh-negative. No naturally occurring anti-D exists; the antibody develops only after exposure to D-positive cells through transfusion or pregnancy.
- Gene
- RHD
- Defines
- Rh-positive (present) vs Rh-negative (absent)
- Natural antibody
- None; anti-D forms only after exposure
- Exposure routes
- Transfusion or fetomaternal pregnancy exposure
Common questions
Why does the absence of anti-D antibodies before exposure matter forensically?+
Because no naturally occurring anti-D exists, a person's Rh-negative status cannot be inferred from antibody screening alone before sensitisation. Rh typing in casework relies on direct antigen testing of red cells, not antibody presence, which distinguishes it from ABO typing where naturally occurring antibodies do exist.
How is D antigen status used alongside ABO typing in forensic serology?+
Historically Rh typing supplemented ABO grouping to narrow the pool of possible donors for a bloodstain, since the two systems are inherited independently. DNA profiling has largely replaced blood-group typing for individualisation, but Rh status can still be relevant in paternity-style biological relationship questions and transfusion-reaction investigations.
Related terms
- CDE Nomenclature (Fisher-Race)
- The modern standard notation for Rh antigens, naming three antithetical pairs: C/c, D (no d), and E/e. Haplotypes such as CDe (R1),...
- Indirect Antiglobulin Test (IAT)
- A two-stage serological test in which IgG antibody is incubated with red cells, unbound antibody is washed away, and anti-human globulin (Coombs...
- Rh-Hr Nomenclature (Wiener)
- An earlier notation system using alphanumeric agglutinogen codes (R0, R1, R2, Rz, r, r', r'', ry) for Rh haplotypes. Wiener's R1 corresponds...
- RHD Genotyping
- PCR-based molecular typing of the RHD gene to determine D antigen status from DNA, including from dried biological evidence where serological red...
- Weak D (Formerly Du)
- A reduced-expression variant of the D antigen that does not agglutinate red cells with standard IgM anti-D reagent in the direct test...