If you know anything about blood types, then you know how they add an extra wrinkle to blood donations. Match donor and recipient blood types incorrectly, and you could even kill a patient. That’s why scientists are working on artificially changing donated blood into type O, the universal donor.
More than a century after their discovery, we still don't really know what blood types are for. Do they really matter? Reporter Carl Zimmer investigates.
Blood types were once thought to be with people for life. And, in almost every case, they're still thought to be with a person for life. But there is one patient whose blood type actually changed. A liver transplant, apparently, has a shot of changing a person's blood type.