A slang term used by blood bank staff to refer to a process currently known as “serum grouping” or “reverse grouping.” In short, the back type involves testing patient serum against A1 and B cells to see what ABO antibodies are present; see the link for serum grouping above to learn more. Blood bankers use the term quite often, and it can be confusing for learners and clinical staff. You may hear it in sentences like this: “There is an ABO discrepancy because the stupid back type didn’t work.”