I find Aerial Gel for cold wash will shift most stains, I often use it to get oily road splash out of my kit. With these biological detergents I like to soak the area, work in the detergent, leave for a few minutes, rinse and repeat as necessary. I don't like to leave a whole garment soaking for hours.
I've also had success with bicarbonate of soda mixed with vinegar.
In both cases with blood I think I'd soak the item cold overnight first. I've no experience with blood stains.