I agree with exlimey in referring to manufacturer's insert. I would also think of resolving ABO discrepancy. If there is Anti-A1 in your patient's plasma, then you have to find type A red cells negative for A1 antigen. In my opinion, it is easier and more practical to use the reagent A2 cells. You have to consider the cost of Anti-A1 lectin and resources used to find A1 negative cells.
So the question is: Do you want to screen and find A1 negative cells or do you want to use reagent A2 cells?