Step 1. Add 'Hand Warm Water' to sink or bowl (Hand Warm Water is the same temperature as your hand, neither Hot or Cold)
Step 2. Add a teaspoon of ordinary Table Salt to the water.
Step 3. Put the article into the salty solution and it's 'Hey Presto' if it fresh and if it has been dried for a while it may take a bit of coaxing with a bit of agitating. When the blood has been removed, wash in the usual manner.
If you are Washing Hospital Surgery Linens or really any linens that have blood on it if you add a pound of ordinary Salt to a 400# load, run the machine for 4 - 6 mins with 'split water temp' do not go over 98 degrees or use a tempering device on a washer, I have not found a washer that can modulate the temperature evenly.
It Is Going to be a trial run to get it right but it you set the blood you can always remove it with Alkali but remember......when using traditional Chemistry you are going to set the Blood.....like is happening now.
The advantages of using Salt is that you are going to 'pull' out the Iron, instead of having it still on the Linen when you go into the Bleach Step and the Iron will accelerate the breakdown of the Bleach and inferior results will prevail.