The conditions to use the item successfully are the same as Worm Food:
You must be in The Crimson. Using it outside of this biome will cause the item to neither work nor be consumed.
You can use the Bloody Spine at any game time.
There cannot be another Brain of Cthulhu present in the world, or the player using the Bloody Spine will take 7000 damage, as well as consuming the item, unless you use the spawnmob command on a server (For example, you would do "spawnmob 266 (whatever number)"
The Bloody Spine is actually easier to get than the Worm Food, as it does not require a second ingredient (Vile Powder is the second ingredient for the Worm Food).