If you want to be prepared for an emergency you must assume (be prepared for) several things 1) You will arrive at the Emergency Room unable to speak for yourself 2) Emergency Room Doctors or Surgeons will transfuse blood based on a standard treatment protocol unless instructed not to by an advance directive or an available family member 3) It is highly unlikely that your primary physician will be part of the treatment team in ER or Surgery. The primary physician might find out about your hospitalization days later or not at all.
Being unable to communicate your wishes you must have something with you that can speak for you - Advance Healthcare Directives or Durable Power of Attorney forms speak for you when you can't speak for yourself. They can tell physicians that you do not want blood under any circumstances or that you will accept blood only after available/applicable alternatives have been used. By taking a blood avoidance posture blood transfusions can often be avoided.