Alloimmunisaation

Alloimmunisation is the immune sensitization of an individual to alloantigens from the same species, most often red blood cell antigens encountered after exposure to non-self antigens through transfusion, pregnancy, or transplantation. In pregnancy, maternal exposure to fetal blood group antigens, especially when the fetus inherits a paternal antigen not present in the mother, can trigger production of IgG alloantibodies that may cross the placenta and bind fetal red cells, causing hemolysis. The most clinically significant alloantibody is anti-D in Rh incompatibility, but antibodies against other red cell antigens such as Kell, Kidd, Duffy, and MNS systems also occur.

Alloimmunisation is diagnosed by screening the maternal blood for unexpected alloantibodies using an indirect antiglobulin test (indirect Coombs test), followed by antibody identification and, when needed, paternal or fetal genotyping. Fetal monitoring may include measurements of middle cerebral artery peak systolic velocity to assess anemia. Prevention includes antigen matching for transfusions and, especially in Rh-negative mothers, Rh(D) immune globulin prophylaxis during pregnancy and after delivery to prevent sensitization.

In pregnancies with a known alloantibody, management focuses on monitoring fetal well-being and treating fetal or neonatal anemia if present. Treatment options may include intrauterine transfusion in selected cases and, after birth, management of hemolysis and jaundice in the newborn, potentially including exchange transfusion. Complications of alloimmunisation include hemolytic disease of the fetus and newborn, neonatal anemia, jaundice, hydrops fetalis, and, in severe cases, stillbirth. Prevention and appropriate transfusion practices have greatly reduced risks in modern medicine.