In the exclusion cell panel, a cell positive for Jka antigens has been set up. What is the rationale for setting up positive controls in selected cell panels?

An anti-Jka control has been set up with red cells that have a single dose of the corresponding antigen (i.e., are from donors who are heterozygous).

If such control cells are positive (as expected), it adds to the confidence that negatives with exclusion cells are valid.