Blood types?

[Ravenshire]

I'm a O+ plebeian... wait a minute that's a  good thing i am a universal donor

O negs are the universal donors. O pos can give to everybody other than O neg. Otoh, you can only receive blood from O pos and O neg.

O neg is the universal donor, but O pos can not give to everyone but O neg. They are limited to other positive blood types. B neg can actually be given to a wider variety than O pos.

AB pos is the type to be if you need a transfusion though. They are the universal recipient.