Principle of DAT
Red blood cells have negative
charged surfaces which repel each other.
IgG attached to antigens on the red
cells are unable to bridge the gap between adjacent red cells to cause a visible agglutination.
Polyspecific antihuman globulin
(AHG) contains antibodies to the Fc portion of IgG and C3d/C3b
If the red cells are coated with
either IgG and/or C3d and/or C3b the AHG will bind to them causing visible agglutination of the red
cells.
If the red cells agglutinate with
polyspecific AHG then the test is repeated using monospecific AHG (anti-IgG) and (anti-C3d/C3b).