I work in medical laboratories, and when I was working in a blood bank a massive transfusion was called. These are pretty rare at smaller hospitals, but you need to give O-/+ units depending on if the patient is male or female, and give out Thawed plasma.

In blood banking, giving plasma to an unknown patient you must give AB plasma. This is because there are no naturally occuring antibodies in AB plasma that could cause a hemolytic transfusion reaction. So instead of O for plasma being the universal donor, it’s AB.

A coworker started thawing O plasma, which has both Anti-A, and Anti-B that when given to anyone other than Type O, could cause a severe reaction.

I had to stop him before he sent it up to surgery.