In one scene, Ted Danson's character tells Nia Long's character that the hospital wants her to donate more blood, as her blood is AB negative, which is pretty rare. True, it is rare, but it's also useless as donated blood, since the only other people who can receive it are other people of type AB - and anyone who is of type AB doesn't need AB blood, they can receive blood A, B, or O.
[Yes, but hospitals like to have all blood types, so they can use the universal blood in emergency situations where they do not know blood type, and use the exact match blood for planned procedures where they know the patients blood type.]
Corrected by pross79
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