G Antigen
The G antigen is present on almost all red blood cells expressing the Rh D or C antigens. It is absent from red cells that are D and C negative. Rh negative patients can produce anti-G antibody following transfusion of Rh negative, C antigen positive red blood cells. Anti-G is a clinically significant antibody that can cause hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. Anti-G is usually considered less likely to cause severe hemolytic disease than ant-D or anti-C.
When an antibody panel is performed to identify an unexpected antibody, anti-G appears as a combination of anti-D and anti-C antibodies. Rh negative patients with an anti-G antibody can be safely transfused with red blood cells that are negative for both the D and C antigens. Therefore, additional adsorption studies are not necessary to distinguish anti-G from anti-D plus anti-C.
The only situation in which anti-G should be definitively identified is when a D negative woman of child bearing age is pregnant and is a candidate for Rh immune globulin. Anti-G may mask the presence of anti-D on standard antibody panels. Subsequent adsorption and elution studies are needed to distinguish anti-G from anti-D. If anti-G is detected, then Rh immune globulin should be given. If anti-D is present, the patient is not a candidate for Rh immune globulin.
Red blood cells with the r” (cE) phenotype are the least likely to express the G antigen because they lack both D and C antigens.
Shirey RS, et al. Differentiation of anti-D, -C and –G: Clinical relevance in alloimmunized pregnancies. Transfusion 1997;37:493-496.
