There is an excellent article in Immunohematology, Vol 16, #4,2000 that decribes the validation of this procedure by the ARC in Columbus, OH. It compard 26 samples using IgG blocking, glycine acid EDTA, and chloroquine diphosphate treated red blood cells in typing for s,S,Fya,Fyb,Jka, and Jkb. The procedure works well with samples that have a w+ to 2+ DAT. One sample tested Fyb+ with the blocking method and Fyb- with chloroquine and glycine acid EDTA treated cells. I remember reading in the insert that chloroquine diphosphate treatment of red cells can weaken the Fyb antigen.