When I was a firefighter / 1st responder, it was drilled into us to never take a military ID tag with blood type as fact. The reason for this that many times a patient could possibly be wearing her/his extended family, friends old military tags etc. With an unconscious patient who has no ID on their person, we would not be able to guarantee that this was their name on the tag and their blood type. Even if the patient was conscious, we were not to take their blood type as fact. Also it very surpising how many people do not know their own blood type. Typical response was " I think...."

This same topic was also discussed at one of our training sessions when we had an ER nurse come in for some training. Her response was to the effect: "No civilian nurse or DR. should never take the risk that the tags are correct and should instead order blood work.