The FDA Guidance on Computer Crossmatching calls out that patients with an ABO typing discrepancy should not be allowed to qualify for computer crossmatches.
" If ABO typing discrepancies exist, you should not rely on a computer crossmatch. This is particularly important if there is mixed field red cell reactivity, missing serum reactivity, or apparent change in blood type following hematopoietic stem cell transplantation. Under those circumstances, your procedures should provide for compatibility testing using serologic crossmatch techniques."
I wrote our policy to include any non-straightforward ABO types for any reason will be required to get an IS or IAT crossmatch.
