I attend a weekly quilting class and one of the students told me that if you poke yourself and get blood on the fabric, to spit on thread or fabric and rub the blood spot. I was not a believer until I poked myself and got a drop of blood on white fabric. I spit (quite a lot) on a piece of fabric and rubbed the spot - the blood went away (not sure where but do not care).
Just thought I would give this tip.