Blood Mage is a cast from hit points archetype meant for sorcerers. I feel that Pathfinder would very much benefit from such a system, and the existing prestige class is not what I would want in either flavor or mechanics. Flavoring of spells is deliberately left vague so that you can decide the specifics of how your Blood Mage casts spells. Maybe she cuts her hand and uses that blood, perhaps she just bleeds when the spell is cast. That's all up to you, and in my opinion, half the fun of playing this class.
On a serious note, the class is far different than what Paizo has built. Your GM may feel uncomfortable with the class (though I think I have the balance tweaked to near perfection). As always, ask first!
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