Serologically weak reactions with Anti D antisera (≤ 2+) should be investigated with RHD genotyping. Pregnant mothers with weak or variable RhD typing and with pending genotyping results should be treated as RhD negative and should receive RhIg. Patients with genotyping confirming weak D type 1, 2 or 3 should be treated as RhD positive. Patients with other weak and variant RHD genotypes should be treated as RhD negative.
For more information:
Flegel et al. It’s time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4. Transfusion. 2020 Apr;60;855–59. PMID: 32163599.
Sandler et al. It’s time to phase in RHD genotyping for patients with a serologic weak D phenotype. Transfusion. 2015 Mar; 55(3): 680–89. PMID: 25438646.