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).