Weak D (Formerly Du)
Definition
A reduced-expression variant of the D antigen that does not agglutinate red cells with standard IgM anti-D reagent in the direct test but is detected by the indirect antiglobulin test (IAT). Weak D individuals are Rh-positive but may be mistyped as Rh-negative in a direct slide test.
- Former name
- Du
- Direct test result
- Does not agglutinate with standard IgM anti-D
- Confirmatory test
- Indirect antiglobulin test (IAT)
- True Rh status
- Rh-positive
- Risk
- May be mistyped as Rh-negative on direct slide testing
Common questions
Why does Weak D status matter in forensic blood typing casework?+
If only a direct slide test is used, a Weak D sample can be misclassified as Rh-negative, which could wrongly exclude or include a suspect or contributor in comparative blood grouping, so any Rh-negative direct result of forensic significance should be confirmed with the indirect antiglobulin test.
Is Weak D the same thing as partial D?+
No. Weak D individuals produce a normal but reduced quantity of a complete D antigen, whereas partial D individuals produce D antigen that is missing certain epitopes, and the two are distinguished by molecular or serologic testing because they carry different clinical and typing implications.
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...
- 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...