RHD Genotyping
Definition
PCR-based molecular typing of the RHD gene to determine D antigen status from DNA, including from dried biological evidence where serological red cell typing is not possible. Can also detect weak D, partial D, and DEL variants that serological methods may misclassify.
- Method
- PCR-based molecular typing
- Target gene
- RHD
- Sample types
- Includes dried biological evidence
- Detects
- Weak D, partial D, and DEL variants
Common questions
Why is RHD genotyping useful on evidence where serological typing fails?+
Dried, degraded, or trace bloodstains often lack intact red cell antigens needed for serological testing, but PCR can amplify surviving DNA fragments from far smaller and more degraded samples, extending Rh typing to evidence serology cannot reach.
How does genotyping avoid the misclassification risk that serology has for weak D?+
Serological anti-D reagents can give a weak or negative reaction for weak D and partial D red cells depending on reagent sensitivity, while genotyping reads the underlying RHD sequence directly, correctly identifying these variants regardless of antigen expression strength.
Does a positive RHD genotyping result always predict full clinical D-antigen expression?+
Not necessarily, because some detected variants such as partial D or DEL alleles produce altered or very low antigen expression, so genotyping results are interpreted with knowledge of the specific variant's known phenotypic effect.
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),...
- D Antigen
- 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...
- 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...
- 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...