A rare challenge in RhD typing

Abstract

Blocked D phenomenon is characterized by a negative reaction of fetal Rh(D) antigens with anti-D immunoglobulin antisera. This occurs because all the Rh(D) antigenic sites are blocked by maternally transferred anti-D antibodies in an Rh (D)-positive fetus. This may lead to incorrect grouping of the newborn as Rh(D) negative. We report a case of blocked D phenomenon in a Rh(D)-positive fetus born to a 29-year-old G2P1 L1 woman at 30 weeks + 2 days of gestation. The mother’s blood group was AB negative, and the indirect antiglobulin test was positive, with anti-D antibody identified with a titer of 1:256. Ultrasound examination of the fetus showed hemolytic features (middle cerebral artery peak systolic velocity 1.59 multiples of the median). An intrauterine transfusion was planned. A fetal blood sample was collected and initially grouped as AB negative. Further evaluation of the fetal blood group was performed using the elution technique, which confirmed the fetal blood group as AB positive.