Rhfactor

Rh factor, commonly known as the D antigen, is a component of the Rh blood group system found on the surface of red blood cells. An individual is Rh-positive if the D antigen is present and Rh-negative if it is absent. The D antigen is the most immunogenic of the Rh antigens and has major clinical significance in transfusion and obstetric settings. The D antigen is encoded by the RHD gene on chromosome 1; some people express weak D variants or partial D phenotypes, which can affect typing and transfusion decisions.

Rh typing is typically performed with anti-D antisera. In addition to D, the Rh system includes several other antigens (such as C, c, E, e), but D remains the key determinant for most compatibility testing in practice.

Clinical relevance includes safe blood transfusion practices and prevention of pregnancy-related complications. ABO and Rh-D compatibility are standard requirements for transfusions. Rh incompatibility between an Rh-negative mother and an Rh-positive fetus can lead to hemolytic disease of the newborn (HDN) due to maternal anti-D antibodies, which can cross the placenta and destroy fetal red cells. Preventive management with Rh immune globulin (RhIg) given to Rh-negative pregnant individuals during pregnancy and after delivery (and after potential fetomaternal hemorrhage) has greatly reduced the risk of sensitization and HDN.

Alloimmunization to the D antigen can also occur after transfusion or pregnancy, leading to anti-D formation and potential hemolysis in subsequent exposures.