I think the blood mechanic fits rogue-like better than Metroidvania. The blood mechanic may be kind of a barrier for map and enemy design, and in my opinion exploration really values in Metroidvania, and keep your eyes on your blood while exploring the map and looking for hidden secrets doesn't sound like a good idea. For rogue-like game, I guess if you want to keep the blood mechanic, you may have to find a stable map-generating algorithm that make sure the player will meet some kind of supplies or enemies in certain distance depending on how fast the player lose blood.
I don't know if this is helpful, but make sure to consider your own thoughts as well, maybe it turns out with more funny experience!