Partial D, weak D types, and novel RHD alleles among 33,864 multiethnic patients:: implications for anti-D alloimmunization and prevention

Background: The D antigen includes category D, partial D, and weak D types, which are important because anti-D alloimmunization can occur in some but not all persons that express a variant RHD allele. At present, there is little prospective information on the prevalence of D variants among obstetric patients and potential transfusion recipients. Study Design and Methods: The RHD alleles were prospectively examined in a large patient population identified on the basis of a difference in anti-D reactivity between two reagents. Results: Fifty-five discrepancies (0.96% of D-) were noted among 33,864 ethnically diverse patients over 18 months, of which 54 represented mutated RHD alleles. Seven obstetric patients were assigned D- status based on serology; only 1 patient had a partial RHD allele. Ten of 25 (36%) obstetric patients and 4 of 6 (67%) female potential transfusion recipients of childbearing age or younger were assigned D+ status, and they expressed a D variant known to permit anti-D alloimmunization. In total 20 RHD alleles were identified including category, DVa or DVa-like alleles (n = 7), DAR (n = 8), and four novel RHD alleles including two new DAU alleles. Conclusion: Given the complexity of D antigen expression, it is concluded that some clinically important D variants identified by standard serologic analysis phenotype as D+ and are potentially at risk for the development of anti-D.