After Jane is shot, the team needs to find blood for a transfusion.
Patterson mentions that they need to find AB- blood group for the transfusion, making it sound as a big deal. It is true than AB- is a rare group, but if Jane is AB-, she can accept blood from anyone with a Rh- blood factor (that is, A-, B-, O-, AB-). And that is not that difficult to find. Patterson shouldn't have asked Rich to find AB- blood, but just any RH- blood. Much easier.