Well, it may be too late if you've already washed it, but there's a few things I've found works on blood:
rinse in COLD water to avoid setting the stain. Use a pre-wash stain remover, like Shout, Zout, or something along those lines. Wash with cold water (and if you like bleach, use it).
If you've already washed it in hot, or dried it in the dryer, it may not come out very easily, but you could try anyway.
Hydrogen peroxide does a good job getting it out of lab coats, but may be hard on a gi.