Testing for presence of A and B antigens on red blood cells:
Forward typing - red blood cells (RBCs) are tested for A and B antigens. Reverse typing - serum or plasma is screened for presence of anti-A and anti-B antibodies.
According to a Circular prepared jointly by AABB, the American Red Cross, America’s Blood Centers, and the Armed Services Blood Program:
The ABO group of all red-cell-containing components must be compatible with ABO antibodies in the recipient’s plasma. Serologic compatibility between recipient and donor must be established before any red-cell containing component is transfused. This may be accomplished by performing ABO/Rh typing, antibody screening, and crossmatching by serologic technique or use of a computer crossmatch.