Rinse in cold water as soon as possible. Then use spray and wash. Let it sit for a while, then wash. Before you throw them in the dryer, check to see if it's all off. If not, use the spray and wash again. Good luck!
Usually Hydrogen Peroxide will take blood stains out pretty good.. (test a small area first to make sure it doesn't remove the dye if they are colored) but just pour it over the stains wait few rinse with warm water (not hot) and repeat until the blood is gone.. small spots that have dried may remain but pour a little on those spots then wash them. It should take it out.
This is gonna sound crazy but it is a TRUE remedy! I learned it from my medical assistant teacher when I was in college! It sounds crazy but it works every time! Not only do I do it but I teach my daughters it also. I swear it will work (for any blood like if you cut your finger) Spit on it. There are enzymes in ones saliva that break down the blood and it WILL come out. The trick is is that it has to be YOUR saliva for YOUR blood, MY saliva for MY blood, MARY'S saliva for MARY'S blood, JANE'S saliva for JANE'S blood, you get the point....... Then wash them. Try it!