This is cool, but be aware that in the ER, we don’t ask you your blood type. And we don’t check you blood type in your records if you need a transfusion. We draw a brand new tube of blood, send it to the lab, and they check it.
Even on horrid traumas that receive immediate blood transfusions, we don’t check the record. We check the blood. And we give them O- or O+ until we know.
This is to be super safe.
No one wants to hear “we gave Joe a life threatening hemolytic reaction bc the computer record said he was AB-, but he’s not.”
Also, there are far more things to check than just ABO± typing. There are a lot of antibodies, and you better get it right.
Lastly, yes, your blood type can change. I have given patients enough blood to change their blood type for awhile - until the new stuff wears out and they make enough blood to have their natural type show up again. That’s partly why, in most US hospitals, a blood type measurement is only good for 2–3 days.