You can easily remove most blood stains from clothing using 3% hydrogen peroxide and a toothbrush. This particular blood stain was on a pair of gray cotton pants.
Supplies:
Steps:
I've been using peroxide to remove blood from garments for years. It does work very well. Your using a pair of grey sweat pants as an example caused me to remember something. Of all the garments I've removed blood from, a grey pair of sweat pants was the only thing where the peroxide actually discolored the garment.
I ended up with huge greyish pink blotches on the pants. No problem as they were for gardening. But if you are removing a stain from a valued garment, it would be wise to test the peroxide on an inconspicuous spot before treating the stain.