The most important are A and B (a set of carbohydrates) followed by Rhesus (a set of proteins, the most important being Rhesus-D)
A = A antigen, no B antigen; AB = both A and B antigens, O = neither; a postpended + indicates a Rhesus-D antigen
Individuals without ABO antigens will develop antibodies against them, which will lyse cells that express these antigens
Individuals who lack other antigens (e.g. D) may develop antibodies following exposure to the antigen.
E.G. An A donor \(\to\) O recipient \(\to\) lysis
Blood grouping
Recipient cells tested with anti-A, anti-B, and anti-Rh(D) antibodies. Presence of a given antigen \(\to\) agglutination by respective antibody
Determines blood type
Antibody screen
Recipient plasma is mixed with specially prepared RBCs
These RBCs are type O, but express various other antigens (e.g. Duffy antigens). Then anti-IgG antibody is added.
If recipient plasma has antibodies against these antigens, antibody will coat the cells; anti-IgG will then agglutinate them \(\to\) positive screen
Cross-matching
Donor red cells are mixed with recipient plasma
If negative antibody screen, this is just a brief check for macroscopic agglutination of donor cells by recipient antibody
If positive antibody screen, then this is an indirect antiglobulin test like above (i.e. anti-IgG is added) \(\to\) slower process, therefore slower release of product from the blood bank