White Pants Blood Stain

I stained on my white denim pants at school (it was so embarrassing, i heard the guys behind me in the hall saying "look" "it's so red. that's gross" and i ran to the bathroom to check and welp...). i don't know how to take it out, currently putting them in the washer on cold but i don't think that'll help. can someone please tell me a way to remove the stain!