Antib

AntiB refers to an antibody directed against the B antigen of the ABO blood group system. It is one of the naturally occurring isohemagglutinins that can be present in individuals who do not express the B antigen on their red blood cells, typically those with blood types A or O.

Most anti-B antibodies are IgM and are cold-reactive, meaning they react best at temperatures below body temperature and generally do not cross the placenta. However, in some cases anti-B can be IgG, which can cross the placenta and may contribute to hemolytic disease of the newborn (HDN) if the fetus has the B antigen.

Clinical significance centers on transfusion safety and pregnancy. In transfusion medicine, anti-B can cause agglutination and hemolysis if a person with anti-B antibodies is transfused with B antigen–positive blood (types B or AB). Therefore, compatibility testing, including antibody screening and crossmatching, is essential to prevent acute hemolytic reactions. In pregnancy, ABO incompatibility can occur when a type A or O mother has anti-B antibodies and the fetus inherits the B antigen from the father; although most anti-B antibodies are IgM and do not cause severe HDN, IgG anti-B can contribute to mild to moderate neonatal anemia in rare cases.

Detection and testing involve standard blood typing (forward and reverse grouping), antibody screening, and, if needed, an antibody identification panel and crossmatching. The presence and characteristics of anti-B influence transfusion decisions and prenatal care in the context of ABO compatibility.