I Want to Drink Your Blood

 refers to an unmarked and repeatable quest in Fallout 3.

After finishing Blood Ties, Vance will happily pay you 15 caps for every Blood Pack you bring him, even though you could have mentioned "donating" them in your conversation (you also had the choice to have Arefu sell them). No Karma bonus is granted. Also, if you go back to Vance after the Blood Ties quest, he can teach you the Hematophage perk, which will make Blood Packs heal 20 HP instead of 1 HP.