The reason the US exports blood products is because it is one of 5 countries that allow commercial blood product harvesting. Well, at least plasma. I don't remember which organization it is, but there is an international organization that tries to get countries to be "self-sufficient" in blood products so that they are not internationally traded (the organization is something like WHO, UN, or Red Cross). Only those 5 countries that allow some level of commercialization actually meet their goals of being self sufficient (and export as on top of that).
Source: A guest lecture at my university by Al Roth, Nobel prize-winner in economics, who is currently focusing his work on these type of markets. Most of his work is on kidney exchanges right now.
Source: A guest lecture at my university by Al Roth, Nobel prize-winner in economics, who is currently focusing his work on these type of markets. Most of his work is on kidney exchanges right now.