Agglutinated red blood cells cannot travel through
the porous structure of paper, indicating a positive antibody–antigen interaction
has occurred. Conversely, non-agglutinated blood can disperse and wick through
the paper structure with the ease to indicate a negative result. This principle has
been demonstrated to detect blood group phenotypes: ABO and RhD. However,
typing for red blood cell antigens such as Rh, Kell, Duffy and Kidd has not yet
been explored on paper.