Hematophage

Hematophage is a Fallout 3 perk. It can only be gained through the Blood Ties quest. It is not possible to take it on level-up.

Blood packs heal 20 Hit Points instead of 1 point.

Obtaining
To obtain this perk, convince Vance to enter into a deal with the town of Arefu by passing a Speech check, a Medicine skill check, or an Intelligence check at the conclusion of the Blood Ties quest. Then return to Vance and ask to be shown the ways of the vampire.

Commentary
Hematophage is definitely worth obtaining if you've completed Blood Ties by brokering a deal. Blood packs can occur randomly, especially in First Aid Kits, and are one of the few restorative items that aren't irradiated. Without the perk, they are relatively low-value items.