I can’t imagine why this is particularly important to do. The next time you’re in a position to need blood given to you, you probably will not be in a state to mention it. And even if you do tell them, they’ll match you anyway..in case you’re wrong or delerious.

If you go to the Red Cross and donate blood, you’ll get a nifty little donator card with your blood type on it. That way you’ve done something good, and found out something you wanted to know anyway.