![]() The Work Group’s findings are described in Sandler et al. The AABB and CAP convened a Work Group on RHD genotyping to develop recommendations for assessing the RhD status of patients with weak RhD typing. In 2014, a survey by the College of American Pathologists (CAP) showed inconsistencies in RhD interpretation across US laboratories, specifically as it relates to individuals with weaker than expected Rh typing. Accordingly, serologic weak D positive expectant mothers were considered RhD-positive and thus not candidates for RhIg treatment. The 10th edition of the AABB Standards, published in 1981, made the same recommendation for expectant mothers for the purpose of assessing the need for RhIG prophylaxis. This was to prevent donor blood expressing weak RhD antigen from being transfused as RhD negative. The first edition of the American Association of Blood Banks (AABB) Standards published in 1958, required serologic weak D testing of donor blood that tested negative for the RhD antigen by direct agglutination. RHD genotyping is changing the way in which RhD status is determined. ![]() However, it is critical to adopt current RhD typing practices to make sure all patients who would benefit receive the injection and at that same time to prevent unnecessary use of the drug. This therapy is highly effective in preventing RhD alloimmunization, with a success rate of 98.4 to 99%. The ACOG recommends that all RhD-negative expectant women receive injections of RhD immune globulin (RhIG) around the 28th week of pregnancy and again shortly after delivery of an RhD-positive newborn. The American College of Obstetricians and Gynecologists (ACOG) reports that without proper screening and prevention, about one out of seven fetuses affected by RhD HDFN will have significant morbidity or mortality. This exposure can cause the mother’s immune system to make RhD antibodies, which rarely affect the first pregnancy however, the presence of these antibodies in the mother’s blood places subsequent pregnancies at significant risk of HDFN if the fetus is RhD-positive. In cases where an expectant mother is RhD-negative and her fetus is RhD-positive having inherited the RhD antigen from the father, the mother may become exposed to the RhD antigen on fetal red blood cells during delivery. Historically, HDFN has been called “Rh Disease” when it is caused by an immune response to RhD with the resulting production of antibodies. HDFN is a condition resulting from an incompatibility between the blood types of the mother and her fetus. The clinical significance of the highly immunogenic RhD antigen was quickly realized, in cases of transfusion and in the diagnosis and prevention of erythroblastosis fetalis commonly called hemolytic disease of the fetus and newborn (HDFN). Over time, researchers recognized other antigens make up the Rh system the “Rh factor” became recognized as the D antigen, now commonly known as RhD. The immune case reported by Levine and Stetson was called “erythroblastosis fetalis” to describe the fetal symptoms that result from the mother’s exposure to an antigen absent on her red blood cells but present in her husband and inherited by the fetus. Scientists have since learned that the Rh blood group antigen described by Levine and Stetson is not the same as the one found in rhesus macaques, and was later named "LW" in honor of Landsteiner and Wiener. Believing these observations described the same blood group, Landsteiner and Wiener named the Rh blood group after the rhesus macaque. Shortly after, Karl Landsteiner and Alexander Wiener described animal studies that discovered immune antibodies made in rabbits by injecting blood from the rhesus monkey reacted with about 85% of human red blood cells the same red blood cells that reacted with the antibody made by the woman above. Her serum agglutinated about 80% of ABO compatible human red blood cell samples. The patient experienced an adverse reaction following transfusion of her husband’s blood after giving birth to a stillborn infant. ![]() In 1939, Philip Levine and Rufus Stetson described the clinical importance of the Rh blood group system through a case of an immunized pregnant woman. An individual’s RhD status is described as positive or negative positive indicates the presence of the RhD antigen while negative indicates its absence.īelow, we explore the history of the Rh blood group and the role of genomics in the determination of RhD status, focusing particularly on the benefits of RHD genotyping for obstetrics patients. This blood group is the second most important after the ABO system. The Rh blood group currently includes over 50 antigens, of which the D antigen is the most important in clinical practice. ![]()
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