Investigation of a neonate with blocked D phenomenon: resolving D type using serologic and molecular methods.

This article addresses the diagnostic challenges encountered and resolution of a neonate with blocked D phenomenon, where maternal anti-D had masked the D sites on the neonate's red blood cells (RBCs), initially resulting in false-negative D typing. This article emphasizes the importance of integrating serologic and molecular methods for accurate blood type determination, which is crucial for managing hemolytic disease of the fetus and newborn. A mother, whose RBCs typed as D- and with a history of D isoimmunization, gave birth to a neonate who presented with anemia and jaundice. Initial D typing revealed the neonate had D- RBCs. The mother's blood sample tested as group B, D- with a high anti-D titer (512). The neonate's direct antiglobulin test (DAT) was strongly positive for IgG, and eluate testing confirmed anti-D specificity, indicating that maternal anti-D was coating the neonate's RBCs. Treatment of the neonate's RBCs with a commercial ZZAP reagent removed bound IgG antibodies, converting the DAT to negative and revealing the neonate's RBCs to be group B, D+, thereby resolving the initial serologic dilemma. Further polymerase chain reaction-based molecular testing of the neonate's RBCs confirmed the D+ phenotype (R1R1), demonstrating the utility of molecular methods in complex cases.