IgG Versus IgM Immunohematology Review 435
IgG IgMStructure Monomer Pentamer
Number of ag-binding sites 2 10
Type of ab Immune Naturally occurring
Optimum temperature of reactivity 37 °C 25 °C or lower
Reacts in saline? No Yes
Reacts best by IAT? Yes No
Complement fixation Moderate Strong
Causes transfusion reactions? Yes Not usually, except ABO
Crosses placenta? Yes No
Causes hemolytic disease of the newborn/fetus? Yes No
Destroyed by sulfhydryl compounds (dithiothreitol [DTT], No Yes
2-mercaptoethanol [2-ME])?