A Case of Weak D Serologic Phenotype

Rh D alloimmunization is the serologic response that occurs when Rh D-negative patients are exposed to Rh D-positive blood. Rh D blood typing is recommended in pregnancy to prevent alloimmunization.

A 27-year-old gravida 3, para 2012 (G3P2012) previously Rh D-negative female presented with discordant and weakly positive Rh D blood typing results. Confirmatory genetic testing revealed weak D phenotype that can be treated clinically as Rh D-positive.

Genetic variants of Rh D can cause varied blood typing results depending on the hospital reporting protocol utilized. If labeled as Rh D-negative, this could lead to unnecessary administration of Rh D immunoglobulin in pregnancy. Genetic variants should be suspected when patients are noted to have blood typing results that are discordant or weakly positive.

Rh D genotyping should be considered when discordant or weakly positive Rh D blood type results are noted in order to confirm and classify genetic subtype.