Role in Blood Banking

1. In vivo: complement can cause the in vivo destruction of rbc following an incompatible blood transfusion if the antibody involved can bind C3 or C9. C3b-coated rbc will be removed by extravascular hemolysis (EVH) in the liver, and C9 coated rbc will be destroyed in the blood vessels by intravascular hemolysis (IVH). [Note: In general IgM is a better binder of complement than IgG because complement requires two Fc fragments close together on the rbc membrane.]

   EVH: All blood group antibodies except Rh and MN can bind C3.

   IVH: Very few antibodies can bind C9. These include anti-A anti-B, and very rarely anti-Le^a, -Le^b, -Jk^a, -Jk^b.

2. In vitro: If clotted specimens are used, complement binding (and indirectly antigen-antibody reactions) can be detected in two ways.

   Antiglobulin Test: Polyspecific antihuman globulin (AHG) serum containing anti-IgG, anti-C3b, and anti-C3d can detect C3b-and C3d-coated rbc.

   Hemolysis in saline 37° tests: These tests can detect C9 binding (visible hemolysis) by antibodies such as anti-A, anti-B, Lewis, and Kidd antibodies (Kidd if enzyme-treated rbc are used).

Role in Blood Banking