From the Research
Weak RhD (Rhesus D) antigen expression refers to a reduced presence of the RhD antigen on red blood cells compared to normal RhD positive individuals, which can lead to variable or delayed agglutination reactions in blood typing and has important clinical implications in pregnancy and transfusion medicine. This condition occurs when genetic variations in the RHD gene lead to fewer D antigen sites on the cell surface or to structurally altered D antigens that react less strongly with anti-D reagents 1. In blood typing, individuals with weak D may show variable or delayed agglutination reactions, sometimes appearing RhD negative in initial testing but positive in more sensitive tests.
Clinical Implications
The management of weak D individuals is crucial to prevent alloimmunization and hemolytic disease of the fetus and newborn in subsequent pregnancies. For pregnant women with weak D, RhIG (Rh immunoglobulin) prophylaxis may be recommended to prevent sensitization if their weak D status is unknown or they have certain weak D types (types 1,2, and 3 generally don't require RhIG) 2. In transfusion settings, patients with weak D are typically managed as RhD positive recipients but may be considered RhD positive or negative donors depending on the specific weak D type and institutional policies.
Diagnosis and Management
The diagnosis of weak D phenotype can be confirmed by RHD genotyping, which can guide the management of these individuals 2. Laboratories should complete RhD testing by determining RHD genotypes (internally or by referral) when serological weak D phenotypes are detected. Individuals with a serological weak D phenotype should be managed as RhD-positive or RhD-negative, according to their RHD genotype.
Key Points
- Weak RhD expression is a reduced presence of the RhD antigen on red blood cells compared to normal RhD positive individuals.
- Genetic variations in the RHD gene lead to fewer D antigen sites or structurally altered D antigens.
- Individuals with weak D may show variable or delayed agglutination reactions in blood typing.
- Management of weak D individuals is crucial to prevent alloimmunization and hemolytic disease of the fetus and newborn.
- RHD genotyping can guide the management of weak D individuals 1, 2.