Blades of Blood

You use your own blood to fuel a magical, claw-like attack. Make a ranged spell attack against a creature you can see within the spells range. On a hit, you deal 3d8 magical slashing damage to the target.
You can choose to 'charge  up' your attack by drawing even more of your own blood and add an aditional 2d8 damage. To do so, roll 3d6. You lose hit points equal to the result of this roll. You must choose whether or not to charge  up before you know if your attack hits or misses.
You cannot cast this spell if you are at maximum hit points, unless you 'charge  up' the spell.
At higher levels. When you cast this spell using a spell slot of 2nd level or higher, the damage of the attack increases with 1d8 for each level after 2nd. The aditional damage of the charged up attack increases with 1d8 for each level after 2nd, but the amount of hit points you lose if you charge  up the attack also increases, with 1d6 for each level after 2nd.