blood is a protein so you need an enzyme product to remove it. You can buy a laundry product, Amaze is one, but I have had better luck with digestive enzyme tablets that are taken to help with digestion. Crush up 3-4 of them, dissolve in enough water to cover the shirt and let it soak. I have had some fabrics that come completely clean, but some blends that still leave a small mark that has faded with repeat washings - I always line dry something like this so the dryer heat never gets a chance to set the stain.
Good luck, hope this will help you!
J
...my son is a chef...cleaning chef whites is a nightmare!!!